I'm just back from NYC, and saw The Tale of the Allergist's Wife (comedy with Linda Lavin) and Proof (interesting and very well-written drama with Mary-Louise Parker, who can do no wrong). Both very recommended if you're serious about good theatre.
On a weekend visit last spring I also caught Contact (the dance musical that even people who hate dance will enjoy), Dirty Blonde (as noted above, funny, sassy, and surprisingly moving; Claudia Shearer stars as well as authored it), Copenhagen (talky and cerebral, but excellent and they cover the little bit of physics you need - its three characters are physicists, but it's "about" finding truth and subjective reality), and Fully Committed (a hilarious one-man satire of the restaurant industry). Also caught two plays that have since closed.
All of these except Contact are likely to be on half-price at TKTS. The downtown location opens at 11:00am and sells both matinee and evening tickets all day; the 47th Street location opens at noon for matinees and 3pm for evening performances. Plus the downtown location lines are likely to be significantly shorter.
[This message has been edited by johna (edited 12-04-2000).]