What is the best method by which to produce caffeine in a pure state?

The easiest way to do it is just to extract it from instant coffee. I used to tutor a first year prac where students did exactly that. They dissolved about 10 grams in water and did a liquid-liquid extraction with DCM, dried over MgSO₄ and would get about 1gm or so of crude caffeine. Recrystallisation with minimal hot ethanol returned about 0.1 - 0.2 gm pure caffeine for most. A more skilled hand would do a bit better, but it's not really that bad and it certainly is an easy way to do it.

Edit: Sonryu, I am happy to go into a bit more of an explanation regarding the experimental protocol and reasons behind why we do certain things if you'd like. Knowing your background, I have a feeling you're going to ask anyway