Raspbmc is an XBMC build for the Raspberry Pi. Recently the developers also integrated the PVR support, which is a truly impressive feat.
In this latest announcement you can check out the current status. Although the Raspberry Pi may be a little underpowered for serious PVR duty, I expect that the TV listing, the integration with various back ends and live TV, will make this a very capable frontend.
The image is from Pete Taylor’s experiments.