If you have not yet visited Woot.com, you should. It is one of the more popular of the "one deal a day" sites that are all over the web. Usually, I check in with a list of these sites several times a week.
Here's the lowdown. Most of these sites have one or two goodies per day at a deep discount. You have to be careful, though. Sometimes there's a reason they are selling items cheap. I always do a search for reviews of a given product, usually on Amazon, before making a purchase.
I scored a very nice Sansa MP3 player for my hubby for $20, and another day found an accessory pack for it for $5. Shipping on every item at Woot is $5, no matter what size it is. These sites are heavy on electronics items, but occasionally have other fun stuff. Woot also has some sister sites, Woot Sellout (scroll down a bit) and Woot Kids. They only have one item per site per day unless they are having a Woot-Off which is a day full of "get them while they last deals". You can tell it is Woot-Off day when there are yellow flashing lights on the home page.
I am also excited to announce that just this week Walmart has started an online daily deal. I have only seen one so far, but it seemed to be a pretty good price. With items that are Site-To-Store eligible, you knock out shipping costs as well. This is certainly one to watch.
Another of my favorites is the Amazon Gold Box Deal. There is one big "Daily Deal", and "Lightning Deals" posted every few hours. Anything is likely to pop up here from movies to groceries to jewelry to software.
There is a useful Daily Deal Tracker that I sometimes peruse if I have the time to do so. I cannot speak for the reliability of all of the sites listed there, though.
I hope you take the time to check out a few of these sites. You never know what you might find!