Wikipedia is a free app that is smart, simple, and effective. Upon launching, a search bar appears. Type something in and boom, there it is in convenient web browsing form. Back on the home page, next to the search bar, is a favorites tab that displays your recent searches. There's nothing more and nothing less. It is the closest I've come to finding the perfect app.
So if you love having access to the near endless trove of data that Wikipedia has to offer and you happen to have a Windows Phone, then you can do no better.