Bib Burglar is a "sniping" tool which basically bids for you in the last few seconds of an auction. Since it's a remote service you don't have to worry about leaving your desktop computer on 24/7.
The interface is very simple. All you need to do is provide the item / auction ID number, the maximum amount you want to bid (it will automatically use the currency of the eBay site) and how many of the items you want.
If your bid is too low you'll get an email to let you know that you are losing, so you can easily increase your max bid.
The only minor niggle is that the system works primarily based on the auction ID, which is probably faster than polling eBay's servers for the item name. So when you get a warning message about a potentially losing bid you've no way of knowing what it actually refers to until you login.
Apart from that one little issue it's a really nice service and you only pay the really low fees based on the items you win ie. if you don't win the auctions you don't have to pay for your bids.
If you signup you can get an unlimited trial account for a couple of weeks. I'm currently having fun abusing mine.