I think of Hampshire College, Evergreen State, Humboldt State, Berkeley, App. State, and to a lesser extent UMass, UVM, UColorado, etc. But as other posters have said, if you're basing your choice of college or university on stereotypical "stoner" schools.... Please don't. Pretty much anywhere you go is going to have weed as others have said.
I have maintained close to a 4.0 during my college career ('bout 3/4 done), and smoked many times daily as a freshman. In retrospect, if I could do it all again I definitely wouldn't smoke nearly as much as I did.
I could never stand the majority of those privileged / spoiled Hampshire students........