A while ago I switched to drinking plain old green tea instead of tea/coffee. Great stuff, feel clearer-headed, more relaxed, more energetic, and more productive. All of the good effects of tea/coffee, but without the unnecessary caffeine highs, lows and tweakiness.
Nice one ;).
I guess I might try switching from black to green.
Caffeine + Theanine together have a synergistic effect - I do 150mg caffeine pill + 300mg theanine pill as soon as I wake up - can't recommend highly enough :)