I use this one, which I picked up on clearance a while ago for about $35. It's a very sturdy stockpot with a sandwiched bottom, which reduces the risk of scorching compared to plain-bottomed stockpots.
If you can use a turkey fryer, I'd consider going for one of those. They usually include a 30-qt aluminum pot and don't cost a whole lot.
The Fiesty(sic) Goat Brewery est. 2007 & Clusterfuggle Experimental Ales est. 2009
Primary: Saison, Berliner Weisse, sLambic I, sLambic II, IPA, 70/-
Secondary: Orange Blossom Mead, Flanders Red I
Kegged: Fat Man Porter w/ 1469, Fat Man Porter w/ 005, Centennial Falcon w/ Conan, Centennial Falcon w/ Denny's, Barrel-aged Fat Man Porter, Belgian Dark Strong, Dark Mild