Nintendo have released an official press CD containing some 336 files ( All print ready, 300dpi, .psd, .ai, .jpg, pdf, tif ).
Many of the images are big enough for posters.
The images and information on the CD cover both the DS and Wii titles, more specifically for the Wii it includes:
Metroid Prime 3
Super Mario Galaxy
Wario Ware Smooth Move
Zelda Twilight Princess
I imagine most if not all of the images are currently available in our gallery, but i'll be having a look over the CD and filling in any gaps we may have.
There's more info on the press here.