Competition must have been stiff if the #1 mobile startup is imgur, a 4 year old website with only moderate success on Android and no success on iTunes.
The #1 startup for mobile, in the overall sense, is Rdio. But we're trying to catch stuff in the way up, so we weigh more heavily toward change in momentum. There is probably another good list I can release later this week that has more of the "usual suspects" you'd expect to see.