With its small and stylish form-factor, great price and decent performance, the Mac Mini is the perfect way to create an HTPC.

Here's how I'm using mine:
Previous gen Mini (1.83 C2D with integrated graphics) hooked up via DVI -> HDMI converter to my HDTV. Using Digital Out to my receiver.

I started with a home built PC but it was big and clunky to use. Most of the other computers in the house are Macs so it was an easy setup/transition.

The Mini starts up quick and instantly adds in some networked drives from my HP MediaSmart Server. It then launches Plex (www.plexapp.com) which is a world-class fork of XBMC that works flawlessly.

Finally, everything is controlled with a Logitech Dinovo Mini which is an integrated keyboard and mouse.

The mini goes in and out of sleep quickly, includes wifi and bluetooth built in, and can be had for a GREAT price (last gen) of $399 in a lot of places.

It's small, stylish and fits in with your other components. I highly recommend it.