Step 1: This is simple
For this you'll need :
1 cheap clip on spotlight (mine came from Ikea)
1 C clamp
1 Daylight flouroescent bulb
Easy really just clamp the C clamp on the rear of the arm of your monitor, you're looking to get it as central as you can. Then fix the spotlight onto the clamp. It's got to throw light evenly behind your monitor when on.
Then fit bulb, and switch on.
Step 2: Here is the bulb I used.
I got mine mailorder, but I've since found that they're not hard to buy at DIY stores
Step 3: Done!
5UKP for Ikea lamp
4UKP for clamp
15UKP for bulb.
So, for around 25quid, I've made sitting at my desk a lot nicer. Shown here behind a Dell 2007WFP