I forgot to post about this a few days ago...
Taiko No Tatsujin DS hs been announced by Namco-Bandai via Famitsu magazine. Source.
There are also magazine scans and a partial tracklisting on this site:
Taikods1 J-Pop:
Natsumatsuri (Summer Festival)
Won't Be Long
Mata Aimashou (Let's Meet Again)
Dance2 Featuring Soy Sauce [Pocky Chocolate Commercial Song]
Children's/Folk Music:
Mori no O-Kumasan (Bears in the Forest)
Inu no O-mawarisan (Dog and the Policeman)
Game Music:
Super Mario Bros.
Taikods2_2 Classical:
Beethoven's 7th (partial)
William Tell Overture
Heaven and Hell (Offenbach)
Flight of the Bumblebee (Rimsky-Korsakov)
Classic Medley (Wedding Songs)
Namco Originals:
Kimi ni Touch!
Mojipittan Medley
Kagekiyo
Pachi O-Sensei
and more hit songs!
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No external (to Namco/Nintendo) licensed music, I guess they need to sort out the licenses before any further announcements...