Just as Andrew says.
I really like my Zotac ION 330, VGA, DVI, HDMI, Optical Digital. I have not tried the HDMI video or Audio myself but others have here on the forums. Netboots without a HD, quiet (the 330 DOES have a heatsink fan, but its quieter than my PS3 at idle), low power consumption (~24Watts idle, ~26 Watts in 1080P decode with VDPAU). I highly recommend it.
The Acer Aspire Revo is a really nice unit in a great VESA mountable form factor with a hard drive and ION graphics, the only reason I didn't go with the Revo was that it did not support the optical digital output I currently use for audio.
I highly recommend an ION based system for a Media Director for use with HD content in a small form factor.