You can use Ferric Chloride solution from your local Radio Shack. This is what I use and it's easy and somewhat inexpensive ($8.95). There are a number of other methods that involve Salt Water Solution, Miracle Grow, Dragon Armpit Excretions and Hydrochloric Acid/Hydrogen Peroxide Solution.
I am going to talk about the Ferric Chloride way....but first some safety tips from Dr Brassy.