The TKTS booth is THE best place to look for last-minute discount tickets to Broadway and off-Broadway shows. Don’t expect to get tickets to the hot new shows, although many of them have insider lists and last minute tickets on their own. You get your pick of whatever they have, so come knowing a handful of shows you’re interested in seeing or be prepared to gamble on a show by title alone. Prices are range between 25% to 50% below the list price, and you don’t get charged those insane tourist markups. Expect long lines, especially in high tourist season, and bring cash or traveller’s checks. You can buy tickets up until the shows open for the night, so this is a great way to go see something on a whim.

Here’s their website:
http://www.tdf.org/tkts/