You'd probably be better off after a couple drinks than using stimulants (I've seen a number of people do much better at DDR when coming back from Beer and Wings night... we called this "Johnny Fevering", after the WKRP episode where Johnny Fever does better at a sobriety reaction test the more he drinks). For a performance enhancing drug, I'd imagine you'd want something more like lorazepam or clonazepam... anti-anxiety medication that will cut out nerves and prevent jumpiness, but still leave you clear-headed enough to play well.
If you want a stimulant... tea is probably one of the better choices mentioned, as it contains theophylline, which is similar to caffeine, but produces more of a mellow buzz than a jolt. It still contains caffeine though.
