Well not much left now except a few fans, the power switch and LEDs, a few PCI cards and some cables.
These are quite handy just to have lying around incase one in your proper computer packs up.
1. Hook it up to batteries
If you live in a area where it sometimes gets hot, these are very useful. Hook it up to a 9v battery or wire it up to USB power
2.Make a hover craft
Isn't exactly the next age of personal transport but its a start. But don't use x3 9v battery's only use
3.Make a air filter
Not a bad idea...
4.Make a better air filter
Better but a bit more complicated
5.Rav them Out!
Power Switch And LED'S
They can't be really reused in a cool fashion but are useful as switches in other projects.