Bidso is a small United States based View Price or Reveal Price auction.  Bidso allows you to earn bids by filling out various offers from their partners, similar to the offer wall in a lot of Facebook games like Mafia Wars.

Flutteroo is a small auction site for United Kingdom residents only.  Flutteroo features 3 types of auctions, Penny Auctions, Lowest Unique Bid auctions and View Price Auctions.

BuyLow Auctions is a USA based penny auction site, where if the winning bid is over $20, they cover the difference to ensure that no item is sold for over $20.  BuyLow Auctions offers a 3 day trial of 10 bids for $4.95 to get started, and monthly discounted bid purchases thereafter.

Snaglo is a medium sized penny auction site based in the United States. Snaglo offers 10 free bids to new users when they make their first bid pack purchase.

Haggle is a large, United States based Penny Auction site open to United States bidders only. Haggle auctions vary in two ways: by the price increments and the time added to the clock.  

BidRivals is a global Penny Auction site, with dedicated sites in over 20 countries. BidRivals has a wide assortment of auction items, offering many features, such as Buy It Now and Use Lost Bids.

Swoopo is one of the best known Penny Auction sites. Started in Germany in 2005, Swoopo has expanded worldwide to the United States as well as South Korea. Swoopo has a very large selection of items and features attracting a large number of users from all around the world. Enter promotion code fb0374 to get 3 free bids at registration.

GoBid is a popular Penny Auction site open to Unites States bidders only. Their auctions are open daily from 6 am to 10 pm Pacific Time. GoBid auctions offer some of the more exciting Penny Auction features, such as Trade Items for Bids, as well as regular promotions to get Free Bids.