FlockOfBirds lets you quickly find relevant, interesting people to follow.
It analyzes the network of people you follow and figures out the most popular people in your network, and the people with similar interests. Then, you can navigate down this list of people you follow and sort their lists of followed accounts similarly, finding new people.
You can also share findings directly from the app. Who are the most popular people in your network? Who were the accounts you followed most recently?