Woot is a site that sells one single item each day. They normally sell that item at a severely discounted price. The quantities are limited and once the item sells out, there won't be a new item until 12am the next day. The item is random. It might be a set of headphones or it might be a 50" LCDTV.
However, at random intervals they will have what is called a "Woot-Off". Whereby instead of having a single item for the day, they have a multitude. When one item sells out, another is placed up right after and this continues until they decide to end it. Once again at random. But what everyone wants to get during the "Woot-Off" is the "bag of crap". It costs a single dollar. But heres the catch, you don't know what it is. You might get a box with a bunch of BIC pens in it or you might get a home theater system.
They also have a shirt of the day which ranges from hilarious to WTF? And then a wine of the day as well. And they also have a partnership with Yahoo! and use this as sort of a secondary woot sale.
http://www.woot.comhttp://www.shirt.woot.comhttp://www.wine.woot.comsellout.woot.com
Overall it ends up being pretty freaking addictive. It's like you're constantly bid sniping on ebay. Most people create an account, fill in all the checkout info for later use, so when they see a really good item, they just click the 'I want one' button and immediately buy it. Because the good items will be sold out by the time you fill all that in.