WikiView is a Wikipedia reader for the iPad. The app allows offline caching (stored on the device even offline until you delete them), quick scroll for fast scrolling, read later queue to identify articles to read later, personalization (font size, type, etc.), look up words by tapping, search, and more. You can read more about the app here.
iPad Notebook 
Wikipanion looks like a better choice to me. Very refined interface with tab bar at left for major headings within the article you are reading. Text is optimized for viewing in IPad. I’m using the free version. Believe there is a paid upgrade with even more features and support for saved searches that you would want to repeat periodically