Currently, I just hook a laptop up to the TV - I know I'm a little behind the times.
I have a cheap TV in the bedroom that can play media off a USB hard drive/memory stick, it can read AVI and MKV, the manual says it can play HD content, but it can actually only decode Xvid/DivX (no h264 - so, really, it's useless for HD).
Considered getting a WDTV and modding it with a firmware to allow it to play disc-based media off a compatible USB optical drive. However, the price is comparable to a standalone BD player with MKV support, which would also have the advantage of being able to play original DVDs and BDs without having to rip/decrypt first.
Anyone use XBMC on a jailbroken Apple TV?