There are two major allures to shopping online. Convenience and price.
RetailMeNot.com looks to solve the latter issue. They offer a fully searchable database of coupon codes for online purchases, many submitted by other users. Search by URL and you'll get a list of coupon codes to use before you purchase an item, along with a description of the discount and a success rate - telling you how often the code actually works. User comments are also available for a more personal recommendation, either about the coupon or the retailer itself.
You can search by tags or retailer. There is also a section for recently popular coupons and retailer sites, as well as shopping forums, an IE toolbar, Mac Dashboard widget and and iGoogle Gadget to keep track of the latest coupons.
Another interesting and possibly profitable feature is their pay-to-post program launched late last year. After a minimum of 10 posts in their forum, you can enter your Google Adsense Client ID on your profile page and earn 50% of the ad revenue for any new threads opened.