The iSight has undergone some minor modifications and now comes with a magnetic mount, compatible with the new Cinema displays. The new SKU is M8817LL/B. The previous model was M9330LL/A.
Otherwise, besides the new magnetic mount and some changes to the plastic attachments, the iSight appears identical.
It's unfortunate that the new H.264 based iChat AV is not yet available. That is coming with Tiger, and will improve image quality dramatically, and will allow multi-user conferencing.