This is something I thought might be useful, but turned out to be semi-useless, but still quite cool. The idea is basic; to use a USB port to run things I might need on my computer desk (such as a fan and reminder lights). With better planning this might actually be a very useful addition to your desk...
You will need:
USB lead with at least 1 plug on it
LEDs x 3 (1 red, 1 green, 1 whatever colour)
Motor and fan blades (I used an old CPU cooling fan)
Switches (1 SPDT, 1 SPST)
Card or something to make the housing out of
Step 1: USB Power and Connections
USB 2.0 ports (the most common version) output 5v DC power at up to 500mah. As long as you stay below the 500mah limit, you can have as much stuff as you want running off it! The circuit diagram is explained in the pictures so I won't go into that here. I will say though, don't use a CPU cooling fan as the airflow is directed outwards rather than forwards (or at least it was on mine). Still, it has some cooling effect. A word of warning though; if you're using a small motor with separate fan blades make sure that it is rated at 5v or you have the correct resistors as most small motors operate on 3v.
Step 2: Housing and Operation.
The housing you see in the pictures is a quick job made from card. It will be updated at some point into a better version, along with a replacement fan. The USB lead is plugged into one of the less accessible ports on the back of my PC (I had plenty spare) so it doesn't get in the way. The reminder thingy is useful if I can actually remember what I am supposed to be remembering (not a dead cert.)...
If you can think of anything I could add to this to actually make it useful, please let me know in a comment, thanks.