Knocked Up... always my go to comedy.
Forgetting Sarah Marshall is a fun one too, pretty much any Apatow produced flick.
Chasing Amy, nearly every John Hughes movie ever makes a good date movie, Happy-Go-Lucky, Before Sunrise, 500 Days of Summer, Eternal Sunshine of a Spotless Mind, saw Going The Distance recently and my girl really liked it, Easy A is surprisingly good, Zack and Miri Make A Porno is pretty funny and kinda sweet in a weird way but definitely don't watch if she is easily offended, can't go wrong with any Pixar movie, When Harry Met Sally, Election is a really underrated flick, I love Groundhog Day it never gets old, Back to The Future Part I or II are classics, Dr. Strangelove is still humorous to me, The Graduate is the king of cringe comedy, Parenthood is pretty good, any Mel Brooks movie is a good laugh, I watched Midnight Run again the other night still hilarious, most David Wain comedies are pretty good...
Idk man, what type of comedy are you looking for?