A fantastic little web site for those of you going to New York City with a limited budget and hopes of seeing some Broadway plays: www.talkinbroadway.com/boards/
This site lists all the shows on Broadway and their policies regarding "Rush" and "Standing Room" tickets. These are day-of-the-show ticket sales that average around $25. Some of them require a Student ID.
The entire web site of TalkinBroadway.com is a great resource for any Broadway fan.