If you're talking about connecting it to a monitor, then you're looking for a VGA cable.
For Wii:
The cable (only one I can find is this one, third-party cable)
http://www.vdigi.com/index.php?page=...chk=1&Itemid=1
Review of said cable
http://wiinintendo.net/2007/10/31/vd...-cable-review/
360:
Official cable:
http://www.amazon.com/Xbox-360-VGA-H.../dp/B000B6MLTG