Rock Band 2 has just been announced. But that's not the good news.
No, the good news is that Harmonix, the makers of the game and its sequel, are not going to turn the original Rock Band into a piece of planned obsolescent junk overnight.
Songs you purchased for RB1 will work for RB2. Future RB songs will work for both games.
Considering that Rock Band is the most expensive game I've ever considered purchasing, almost as expensive as a Wii, this is very good news for a game that's made downloaded content one of its cornerstones.
There's plenty more description of new features and better hardware at the link above. Fans of Rock Band, and those who purchase its downloadable content for Xbox or Playstation, should also check out Chris Grenard's comprehensive Rock Band Downloadable Content Database for thorough reviews of all of the songs available for purchase.