This idea started with me trying to put all the Guildmages in a single deck, with ways of generating tons of mana (e.g. Mana Echoes), and helper cards like Training Grounds.
I made sure each of the Guildmages had something to do (e.g. I put in cheap instants/sorceries for Izzet Guildmage).
I use Sliver Queen to help generate tons of mana (the tokens can be used with Earthcraft or whatever). There is a fair amount of potential for this deck to go infinite, so be warned if you find that sort of thing distasteful.
Yeah, I know I use Sliver Queen in a lot of my deck designs, but for this deck it is really helpful. (In fact, this was the deck that caused me to re-evaluate the need for 5 color / Sliver Queen in a lot of my other theme decks.)
Click here for a text version of this decklist
Click here for my EDH Commander decks