Well, from how often they're showing up on lists, I can see that I have a few plays with which I must make myself familiar! I don't know from THE MAN WHO CAME TO DINNER or even BAREFOOT IN THE PARK, which seem to be popular choices today.
For those I do know, I have to add yet another vote for NOISES OFF, simply one of the funniest things ever written, IMHO. Like JRand, I'm also a great fan of David Ives and his "All in the Timing" set of play-lettes, particularly THE UNIVERSAL LANGUAGE, SURE THING, and THE PHILADELPHIA.
As for LEND ME A TENOR, I saw it probably 12 years ago or so, and I don't really remember it all that well. I remember finding it amusing, but nothing all that great.