Now tho my favorite rhythm games are usually found in the arcades such as PIU series, DDR series, and MaiMai Series (Sega rhythm game. I encourage you guys to check it out if it's available in your local arcades because I think it's only available in Japan and some Asian countries)
All I liked are the Ouendan games for the Nintendo DS, DanceDanceRevolution, and GUITARFREAKS.
GUITARFREAKS is like Guitar Hero, but it uses 3 frets instead of 5, has a smaller timing window, has a wide variety of genres, and contains Konami original songs, which some are also in DDR (like "Venus" from V3 and "FIRE" from the first GF).
I highly recommend the whole rhythm heaven (rizumu tengoku if your trying to find the japanese exclusice(s)) it's absolutly fantastic and packed to the brim with content and fun.