While we like to showcase the "big" apps here at WPCentral, we can't forget the thousands of indy develoeprs out there.
WikiRand is one of my new favorite apps due to its simplicity and feeding on my unsatiiable quest for odd knowledge. The program adds a Tile to your start screen and it randomly downloads articles from Wikipedia. It then displays the image from that article and title, giving you a sneak peak.
The app automatically updates, though I'm not sure how often (looks to be every hour) and wile you can turn that on/off, you can't set the interval. It doesn't use much data as the article is only downloaded if you click the tile. It can take a few seconds to load over 3G but it's fast over Wi-Fi. Other than that though, for $0.99 (Try-before-you-buy is available) you can't beat it.
Highly recommended for you wiki addicts.