This kind of homemade USB plug could also be used for other things, like repairing USB cables.
Step 1: Supplies
A Soldering Iron
150-200 Grit Sandpaper
Blue LED (Other colors will work just fine, too)
Small Piece of Perfboard
I used a 1k resistor because I just wanted a nice looking light, not a blinding one. ;P Feel free to use a different value if you choose.
Step 2: Score and Sand
If your piece of perfboard isn't already in a strip like mine, cut some out by scoring the perfboard with your X-Acto knife, then breaking it apart.
Take your strip of perfboard and score it four traces in with your X-Acto knife (Four USB pins = Four traces). Break the piece off so you have a squarish piece that fits in a USB port. If it does not fit right, sand it a little bit to make it the right size.
Step 3: Bend and Cut
Bend the positive lead of the LED 90 degrees out, and bend one of the leads on the resistor down and out, so it will line up with the bent LED lead. Check the pictures if you're a little unclear on what to do; after all, they ARE worth a thousand words each.
Clip the leads down so that there will be enough left for soldering, but clip them enough so that they will not get in the way of anything. Make sure everything lines up with the two outer traces on your perfboard, like in the second picture.