My most common non-guaranteed uniques: Hell staff (8), followed by Anti-Freak Jackal (6), Cybernetic armor (6) and Hellwave pack (6). The only uniques I have never, ever seen are BFG10k and the Scythe.
Most common non-guaranteed exotics: phaseshift boots (11), medical armor (10), shockwave pack (10), phaseshift armor (8) and finally a weapon, minigun (7).
On a funny note, medical armor is more useful than medical power armor, because it's moddable (you can get rid of the speed reduction and achieve a similar amount of armor), but even then it's a bloody waste of inventory space. Ok, it might be useful if you can afford a breather between getting nearly killed and taking the medpack you should have in your inventory. If you don't, you're still very likely to get insta-gibbed even if you can get your health up to 20%.