Nintendo opened a teaser website for Wii's Rhythm Heaven today. There's nothing at the site except one major news bit: the game due for release on July 21!
One other little bit from the official site. The game's final Japanese name isn't Rhythm Tengoku, but Minna no Rhythm Tengoku, or Everyone's Rhythm Heaven.
Rhythm Heaven was included in Nintendo of America's E3 lineup this year. You can see the screens and trailer footage below from the show below.