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
Planned: sLambic II, Flanders Red II
Primary: Fat Man Porter, Orange Blossom Mead, sLambic I
Secondary: Flanders Red I
Kegged: 3 different ciders, Janet's Brown, Barrel-aged Stout, Hallertau Blanc Pale Ale
Bottled: Flanders Red I