I talked before about how I believe this to be one of the most important cards in standard right now, and I still feel that way. It powers up green-based decks into the three color area quite easily, as long as your multiple-colored-mana requirements are not too harsh. (Farseek doesn't power up a RRBB Rakdos, Lord of Riots casting cost very well, but it sure turns on the ability to cast Searing Spear and Oblivion Ring and Inspiration and Ultimate Price)
This is because our Farseek is going to be searching out basically a dual land, and though this dual land can tap for one of two colors, it cannot tap for both of those colors at the same time.
Because Farseek costs Green to cast, the best way for it to work as fixing is if our three colors include a Ravnica Shock-Land that is of two NON-GREEN colors. Once Gatecrash comes out, this will be a non-concern, but for the next 2-3 months, this is not ignorable.
If we go Farseek into Temple Garden (taps for G or W), we get our dual land, but we don't get full three-color fixing out of it. If we go Farseek into Blood Crypt (R/B) and are G/R/B as our three colors, we get full three-color fixing with our one fixing spell cast. This means what is most important are the non-green duals.
The Non-Green Ravnica duals ("shock-lands") we have so far are:
So, the three color pairs (again, until Gatecrash makes this all irrelevant) that make the most sense from Farseek-fixing are:
Red-Black-Green (Jund)
Red-Blue-Green (RUG)
Blue-White-Green (Bant)
I see a lot of people playing "Junk" (Green-Black-White). They play their Farseek off Forest-Forest, and get a... Oh wait, I can't fix my mana with Farseek, because all I can get are Temple Garden (Green-White) or Overgrown Tomb (Green-Black), which doesn't fix both of my colors. Junk has some powerful spells, but the mana just isn't as good as it could be for now.
Of these three, RUG has only one Ravnica shock-land at this point (Blue-Green, and Green-Red are in Gatecrash). That is not a mortal wound to this color triad, because like we said, green-fixing via Farseek lands is not the most important. However, Bant or Jund have 4 more potential lands that can tap to cast Farseek, while also fixing one of the two other colors, as well as being fixing during those games when you don't draw Farseek.
So, I would encourage focusing on the two "shards" (Bant and Jund) rather than the "wedge" (RUG) for the time being.
Again, we're looking at a mana base that is 12 M10-like duals (between M13 and Innistrad), 4 Farseek, 1-4 Shocklands of each type (depending on how much multiple color we need), 1-4 Innistrad block lands that tap for colorless, and Basics to fill to 24-26.
It is quite reasonable if color requirements are relatively light to play only one or two of each shockland, just to find with Farseek and rarely take two damage, if your spells look like Thragtusk or Sever the Bloodline. (lots of colorless)
If your spells look more like Rakdos or Call of the Conclave however (little colorless to be found) upping the shock-land count may be warranted.
Another thing to consider is that with any shockland in play, ALL 12 of your Innistrad/M13 duals come into play UNTAPPED! This is pretty huge (and another selling point for Farseek searching out a dual)
Once (if) we go to four-colors, this will no longer be true necessarily, but for three color mana bases, we are good to go with any shock-land in play. If we overdo it on shock-lands though, our mana may come into play tapped because they are shock-lands and they are painful, rather than that the lands themselves come into play tapped by game-rule...
How much fixing can we get?
If we max out on colored mana, for color group ABC, we use:
4x AB M10
4x BC M10
4x AC Innistrad
4x AB Shock
4x AC Shock
1x A Basic
1x B Basic
1x C Basic
1x Some utility land.
This mana base gives us a almost shocking 17 sources of A, 13 sources of B, 13 sources of C. This is better mana than a two-color mana base with 12 of two different basics.
A more conservative (less life paid) mana base would look something like:
4x AB M10
4x BC M10
4x AC Innistrad
2x AB Shock
2x AC Shock
1x A Basic
1x B Basic
4x C Basic
2x Some utility land.
This gives 13 sources of A, 11 sources of B, and 14 sources of C. This is 5 less colored sources (one more utility, 4 less shocks), but we still have in the neighborhood of half our lands that tap for any color.
Which way I'd go would depend on how mana-intensive our spells are, and how much early game multi-color we need. We also need to consider that farseek is effectively four more sources of non-green, if we have green. This pushes the number of sources of each color to pretty absurd levels.
Keyrunes
We also have the possibility of using Keyrunes as mana fixing/acceleration/creatures, but green decks just won't need it as much as, say, a Red-Blue-Black (Grixis) deck would need, because farseek fills this role a bit for us. Farseek is cheaper, which is huge, and on-demand double-fixes (you don't have to have the "Right" Keyrune in your hand at the time). It also doesn't open us up to most any type of removal. The Keyrunes turning into creatures late game is relevant, but hopefully we get our late-game utility from the Innistrad block utility lands. (Let us use our mana once we've run out of other stuff to do)
Utility Lands
To wrap this post up, since we've been going for a bit now, lets think about the last aspect of mana, the colorless Innistrad block lands ("utility lands")
Cavern of Souls is the first utility land that comes to mind.
I call this a colorless land, because, well, 90% of the time it is going to be tapping for colorless. It doesn't fix mana for non-creatures, it doesn't cast Farseek, it doesn't tap for colored mana for more than half of your creatures, it just doesn't tap for colored all that often. What it does to is make sure that a particular creature spell that is critical resolves. (Presuming you knew what creature spell was going to be critical when you played the Cavern)
Syncopate at least is going to be played in standard. Snapcaster Mage will flash it back. People are not going to play around counterspells, which is the best time to be playing counterspells, especially two-mana ones. If our big plan is to cast a Olivia, Angel of Serenity, Thragtusk, or Niv Mizzet, and we die if it doesn't resolve, Cavern is worth thinking about.
Maybe it's a sideboard card, since it really hurts our mana base in general, but it needs to be kept in mind.
Other colorless sources that are not the Innistrad block utility lands (Cathedral of War, Rogue's Passage, Hellion Crucible, Grove of the Guardian, Ghost Quarter) really don't make the grade. Unblockability, coming into play tapped, and making a pretty average guy is not what we're looking for out of a land in a multi-color deck. Grove is particularly bad, because we need the land to function when we don't have an overwhelming board presence. Grove is also weak to Unsummon, a card we should be relatively resilient to. (We're not going to tap two Thrag's to make a 8/8 either)
Green requirements:
Alchemist's Refuge is playable in Bant (GWU), but it is not terribly exciting. It does let you play Sorceries and Planeswalkers at instant speed (I initially read it as just creatures), but planeswalkers are actively bad to cast at instant speed. It does increase the costs of the spells by 3 (UG, and tapping the Refuge), so I would not put this at the #1 slot in terms of usefulness.
Kessig Wolf Run is a well-known pillar of standard magic. It turns x mana into x-3 damage when you have nothing else going on. It gives trample to get past chump-blockers (spirit tokens). It makes all of your guys into individual threats, which is strong against sweepers. It is particularly good with Thragtusk, since he has a high power, and leaves a guy behind after he's removed, so you get to pump multiple times for strong effect. This is easily one of the best utility lands in standard.
Grim Backwoods has not seen play in any deck that I've seen, outside the commander format. It just costs too much mana, too much resource, just asks too much of you for what it offers. I love Black and Green, but this is one of the worst utility lands from this cycle.
Gavony Township on the other hand is one of the best utility lands in standard these days. It snaps the neck of the mirror match, it gets your guys out of range of damage-based removal, and it adds a bit of damage each turn. If the board is stalled at all, Gavony Township will take the game away. Restoration Angel tends to lead to board stalls, and opposing Angels can stop yours due to their power being less than their toughness. Gavony Township fixes these problems though. It is at it's best with mana creatures (since they tap to activate it, and are pumped by it), but it is still good with any setup that involves creatures and a stalled board.
Non-Green requirements:
Moorland Haunt was a staple of standard for quite some time in the Delver decks of yore. It is good at getting the final few damage in, re-using your cheap creatures, utilizing self-mill, and extracting maximum value from your creatures. It also has the cheapest activation cost (yay... go UW), which is quite important. However, in a Bant deck, you end up re-using your creatures with Angel of Serenity, or your guys are so big they win the game on their own, so it is not a good tactical fit with the Bant strategy.
Stensia Bloodhall is the epitome of grinding. It has the highest activation cost, and one might say the least effect. Why doesn't this drain your opponent for 2? CMON! Anyway, likely not for us, since we're winning with 8 point swings, not 2 point pings over 10 turns.
Nephalia Drownyard is a great card against control, but not for this deck strategy.
Vault of the Archangel is conceivably the best card for this archtype. It is probably the best justification to go BWG ("Junk"), as it works particularly well with Lingering Souls. Unfortunately, it doesn't fit well with our mana requirements. Life gain is strong vs the aggro decks. Deathtouch is probably less relevant, but as we move into the 4 color Green world of Gatecrash, we should remember that this exists.
Desolate Lighthouse is a fine card, but I'd probably rather play 1-2x Faithless Looting, than 1-2x Desolate Lighthouse. Also, it is RU, which only works with RUG in the above triads.
Slayer's Stronghold is an incredibly aggressive card, and it makes all your late-game draws live. Unfortunately, it's not in any of our color pairs.
The top contenders are definately Cavern of Souls, Gavony Township, Vault of the Archangel, and Kessig Wolf Run.
That's all for today, thanks for reading!