So many of the ones I thought of have already been noted.
Have you seen "The Princess Bride"? It's nice for silly escapism. Always makes me laugh.
I saw "The History of the World Part One" recently and while I don't know if I'd *recommend* it per se -- some is great, some ain't -- it reminded me of how much I like Mel Brooks. I think "Blazing Saddles" and "Young Frankenstein" were already mentioned. I just went looking for others and found this:
http://www.afi.com/tvevents/100years/laughs.aspx
(It's "A Fish CALLED Wanda" not "A Fish NAMED Wanda" btw. Loved it.)
Another movie I enjoyed recently (that I also mentioned recently) was "Holes." It's for kids but has some amazing comic performances by Jon Voigt and Sigourney Weaver, and a supremely satisfying plot. Not primarily a comedy but good escapism. I had very low expectations when I started watching it and it may have benefited from that, might not stand up to high expectations, I'm not sure. But I enjoyed it.