I don't think we've posted about this yet, A while back foxmiles brought this to my attention: Raspberry Pi
Its a fully featured ARM based computer. it has a 700mhz processor, and your choice of a model that has
either 128MB ram and no ethernet controller.
or 256MB ram and a wired ethernet port.
It has HDMI and RCA out with a VideoCore IV GPU (Does high level 1080p h.264 Decoding), USB and uses SD card as its hard drive.
They have models available from $25 and up.
The possibility's are really only limited by your imagination. $25 completely silent (fanless) Media center pc. Tiny web server. hardware firewall.... the list goes on and on