Anniesbid is one of the older penny auction sites- they've been around for 3 years and I've bid there on and off over the years. I like the fact that they support charities and have all kinds of competitions on Facebook and Twitter to get free bids. Sometimes they take a day to respond to support requests, which is why they get 4 stars instead of 5 from me. But I've always received what I've won and the team there does a great job of making the bidding experience smooth.