9to5Mac identifies the next generation Apple TV as codename "J33" based on newly found references from the iOS 5.1 beta. Previous references had pinpointed the "AppleTV3,1" in earlier versions of iOS 5, which appears to be the corresponding product id. The "J33" codename doesn't provide any more information about the device, but just provides an extra little hint that Apple is working on a next generation device.
A new Apple TV could integrate Apple's new A5 processor, which offers much faster graphics processing, and include true 1080p support. But unless Apple plans on offering 1080p content on iTunes, that feature would be of limited use to the majority of consumers. Fortunately, Apple has been rumored to be prepping movie studios to start submitting 1080p content to iTunes.