Check out Youtube's Free with Ads movies. Seriously. They've got a good selection of great movies (especially comedies) from the 80s and 90s on there.

Naked Gun series, Oh Brother Where Art Thou?, Raising Arizona, Idiocracy, The Terminal, Major League, Top Secret!, Hot Shots!, Beavis and Butthead Do America, The Terminator, Delirious, Robin Hood Men in Tights, Captain Ron (crap, it's not free anymore), original Robocop, Secret of Nimh, Ghost, I'm Gonna Git You Sucka, Silence of the Lambs, Teen Wolf, to name a few.

It's a smaller selection and they don't seem to stay Free for more than a few months, so you have to keep checking it, but there's some good stuff on there.