I'd like to be able to view completed auctions of a particular item, so I can see who has been selling a particular item and to see what the general sales price range has been in the recent past. This would be especially helpful if there are no instances of a particular item in the auction house when you want to post something, and you're not sure what price range the market can support. (While I recognize that ours is actually a marketplace rather than an auction house, I'll note that eBay gives you the ability to search for completed auctions over the past month.)