I recently built a penny auction site for a client, after attempting to build it from scratch I realized its a lot harder than I thought to make sure it all works perfect under load. So I turned my attention to finding a company that sold penny auction software. There are a fair amount of companies out there, so be warned, most are selling garbage scripts!
Some companies had descent software but when problems did happen, their support was so unresponsive that it was a deal breaker.
To make a long story short, I stumbled upon Indeva Web Solutions in LA, they have a product called Indeva AuctionPro. It does Penny Auctions, Reverse Auctions, and some other stuff too. Price was good, service was excellent, software was perfect. I would recommend you look into them: www.PennyAuctionBusiness.com