BigDog is right, you want hi GI carbs after your workout, because they are more quickly absorbed by your body. Dextrose and Maltodextrin are both good choices and should be available at most health food stores for less then a buck a pound.
Whey is also a good protein source right after your workout, because it too, is quickly absorbed. I usually make a shake with about 50 grams of dextrose and 30 grams of whey. When I'm bulking I'll use more dextrose, and when I'm cutting I'll use less.
However, with that said, I still like having oatmeal for my postworkout meal, especially when I'm out of dextrose. I haven't noticed any difference really.