I'd wait for the Raspberry Pi, the only commercial set top box that equals XBMC in some ways is the Boxee Box
because Boxee is itself a fork of XBMC but it is much more locked down and simplistic.
None of the other media players on the market powered by Sigma Designs (WDTV Live, Popcornhour, Dune) or Realtek chipsets (tons of no name players
) come close to XBMC in terms of GUI or features.
Sigma Designs are porting XBMC to their next generation chipsets but you wont see them anytime soon they were due last year and probably wont come till end of this year at best.