Since getting the entirety of their archives online doesn't seem to be a priority (as opposed to, say, getting their ass kicked by The Onion, College Humor, and, shit, 4chan in any objective measure of humor quotient and cultural influence), I scanned in a few of the more interesting illustrations -- the full set, which I'll probably be adding to, is on Flickr: Harvard Lampoon Illustrations from the 1990s.
First, a few items I'd photocopied (in the pre-digital era) for wall decorations:
Superhero comic strip parody, Vol 182, Issue 3 (Fall, 1992): "Got to push the button before Dr. Bad Guy destroys the planet! Gotta do it! Gotta do it!"
Vol. 182, Issue #4 (Winter, 1992): "The Wonderful Treasure in Every Light Socket Which You Can Get Out With a Fork."
Next, a couple of items from the Lampoon's Monday Poster Series:
Lastly, here's not an illustration, but an actual advertisement, for some upstart humor publication at some podunk state school that will never amount to anything: