Like the Boxee Box remote control showed us, a remote for a media center (or HTPC) only needs a few basic buttons. Unfortunately the Boxee remote is not sold separately but the GlideTV Navigator might be a good alternative. It's a small remote control that fits in your hand, connects through a wireless USB dongle and let's you control all the basis functions of a media center. GlideTV themselves call it a 'couch mouse' and that could actually be a pretty accurate description. It has a trackpad in the middle and some (media center oriented) buttons around it.
Prices are around $149,- or €129,-. An unboxing video is shown on testfreaks.com.