DreamScene is also pretty cool if you have the CPU for it.
desktop.wmvBasically, run HD WMV's as a background.
I have a 2.0 Intel Dual core, it idles at about 50% with dreamscene running.
You can right click your desktop and pause it though, if you're going to go in-game or something.
If you're running Aero though, it fucks up icon text. Note how they're all transparent, and only the border is visible.
Not a big deal imo.