In a new press release issued today, Nintendo of America has confirmed that Pixel's popular platformer will be arriving on the WiiWare platform this coming holiday. No specific date or price revealed yet, although it's stated that the game will feature new and exclusive content not found in the freeware version. (source: Joystiq)

Nintendo's Press Release
Rumor: Cave Story on WiiWare (July 2008)
Cave Story Wii official site