We told you before that one of RIM’s employees, @gordtanner, that came from their TinyHippos acquisition was working on a Wikipedia app. Specifically he was porting their HTML5 open source app to work on the PlayBook through PhoneGap. Now that app is officially in App World directly from the Wikimedia Foundation and is totally free.
The font size is a bit small for my taste but definitely makes browsing Wikipedia much easier. Update: You can change the font size in the settings to be easier to read.