If you're done playing New Super Mario Bros. Wii—released18 months ago so you may well be—you could always try the fan-made Newer Super Mario Bros. Wii.
Currently in development by a team of devoted modders, artists and Mario fans, Newer Super Mario Bros. Wii. is an unofficial sequel of sorts to Nintendo's 2009 retail release, and boasts over 100 new levels, new art, new maps, new enemies and even new "gameplay mechanics".
The team are hoping to release the "game" (expansion?) on November 16, 2011, with downloads able to be played on "any homebrew-capable Wii console without piracy or ISOs."