Wireless Network Adapter
It's hooked up to a 50" TV in the living room, so it's mainly used for the Home Theater aspect of HTPC, and for gaming. Have two PS3 wired controllers hooked up to it as well.
Using the stock CPU fan that came with it, have designs on replacing it very shortly. Temps are way too high, the CPU isn't even overclocked and only rated for 65°C.
EDIT: Just purchased an aftermarket cooler for the CPU. We'll see how it goes.
EDIT: Went awesomely! Can barely hear it even at CPU max load, and temps went from 44 idle/66 load to 28 idle/48 load!
EDIT: Removed the motherboard listed since this site didn't have the exact model purchased, and previously went with the closest model. Fixed, and listed as Custom.