Out in the Marketplace there are quite a few Wikipedia apps. Everyone tends to have their favorite and I found mine after having gone through the bunch. It's Wikipedia Search.
Reason? It's fast, minimalist, elegant and to the point. Plus it's quite powerful with those options I'm looking for (mobile view vs desktop), dynamic search, multi-language support, etc.
It's not free (not many of the Wiki apps are) but at $0.99 it was a no brainer for me. Check out the vid to see why and grab yourself a trial version here if you want to take it for a spin. Oh and look for some full reviews of other Wiki apps soon. Finally, check out our WikiRand video for some live tile randomness.