If it's not horror, it should be old. Classic and retro are what I go for. Especially comedy.
The Odd couple (1968)
One of my favorite movies after just one viewing. Fantastic cast, Lemmon and Matthau, the great comedy team at their best. Spectacular screenplay, great lines, and visual gags. The whole thing is stunning.
Who done it? (1942)
Abbott and Costello were one of the best comedy teams ever, even if they didn't get along off-stage... Their only film sans musical number. The Watts and Volts bit was good. I especially like the line said when Who's on first? was on Costello's radio. Something to the effect of "I hate those guys".
It's a mad mad mad mad mad World (1963)
Everyone who was anyone was in this. You could sit there watching it and point to the screen every five seconds going "OOH, OOH, I know that guy!" I liked it.
Soylent Green (1973)
What a downer! It's a fine film, but pretty disturbing. Everyone ought to see it before someone spoils it for you. I don't know if it's considered drama, sci-fi or horror. It seems to be all three.