Typical USB pin out is:
+5V, Data -, Data +, Ground, Ground or Key.
Each of the +5V leads can be used for up to 500mA (half an Amp) of juice (2.5W) so why not use it if your motherboard has a gajillian USB header sets on it?
First, pop all of the wires except for the red (+5V) and black (ground) on your typical USB header cable. This can be something you bogarted out of a retired case or one of those header brackets that comes with the mothreboard.
Since your typical USB header consists of two USB ports, we can wire both +5V and both ground wires up so we can deliver 5W to a Molex. The Molex can be used to power many +5V devices. I've used mine to power front panel LCD's or internal flash drives.
On the other end, I just pull all of the wires out of whatever they're hooked up to, decapitate all but the red and black and crimp on the Molex pins....
Of course, you can also just solder up the wires directly to other parts that may not come with Molex connectors like little LED's, etc. Don't be shy! Just don't exceed the 500mA per port rating!