Canon uses different codenames for the same camera body depending whether it is sold in North America or Europe. In Europe we have the 50D, 550D and so on, while the US has XTi (or something like that).
Most of the questions on this site just refer to the names they're familiar with, so it would be useful to have a post to refer to which can translate the names. I'm making this CW in the hope that this will be updated as new models come out.