Ok...before 1990...
I saw W.C. Fields in http://en.wikipedia.org/wiki/The_Bank_dike a couple of weeks ago...
W.C. Fields was so funny!
Yep, I need to see some of his movies again now that I'm all growed-up. He was an incredible juggler as well!
For an old movie that I like, most of the "US is the best" style WWII movies fit my bill such as The Longest Day and In Harms Way.
Other movies, since you consider old being pre1990:
Blazing Saddles, The pre-cross-boarder portion of Stripes, Animal House, Young Frankenstien (Schteen!), 1-2-3 (quick banter), To Kill a Mockingbird, The Man Who Shot LIberty Vallence, Arcenic and Old Lace
I'll stop there
edit: crap, haven't seen most of those for the first time LOL