The Wikipanion app is one that I use often, and I'm always on the lookout for good reference apps. Hyper Facts ($0.99) is a new offering that gives you access to Wikipedia in a new way, in that it highlights the categories and infoboxes associated with each article as well as giving links to related information. It also integrates locational information and maps. You can do a search by person, location, event, or work (e.g., a song title), or you can search All. The Nearby feature is pretty cool.