The winner of this week's Android Arena was an app Gina Tripani chose: StackExchange. This is the official Android app for the Stack Exchange website, which is a network of over a hundred Q&A sites including Stack Overflow, Super User, and Server Fault. Full disclosure: Gina's ThinkUp co-founder is on the board of Stack Exchange, and she knows the developers.
The StackExchange app allows you to track all of your interests in a single place. You can answer questions, vote questions up or down, search or browse by tag, and get instant notifications when you get a new answer or comment.
You don't even have to log in to use the StackExchange, either. If you don't log in, it will just show you a feed of hot questions across all of the sites. Once you have logged in, you can customize the app and add the sites you like the most.