I've seen Drugstore Cowboy...it was pretty good I also saw Blow besides these two, tell some good films bout drugs (i prefer films about addicts/drug users, don't like that much those about drug bussiness)
If you like movies about drug addicts, then check out the following: Candy Requiem For A Dream Basketball Diaries Trainspotting
Candy is a great movie. Just saw that one... Actually, all of those are good recommendations TNStoner