Consumer Reports has a good article on pressure cookers that you might find helpful if you’re looking for one.
I don’t think you can go wrong with a Kuhn Rikon and my favorite place to buy these type things is Pleasant Hill Grain. If you’re wanting to get one that’s a bit less expensive, go with a Presto but I do not like the aluminum ones as much as I like the stainless steel Presto models. Lots of places, even Wal-Mart, have Presto but the only one I saw at our Wal-Mart was aluminum. Target has a Presto 6 quart aluminum pot for $29.99, the 6 quart stainless is $79.99 ($59.97 at Wal-Mart.com) and the Kuhn Rikon 5 liter (5-1/4 quart) at Pleasant Hill Grain is $219 or the 7 liter (7-1/3 quart) is $249. Big difference in price but in my opinion, there’s a big enough difference in the pot to make the price difference worth paying.