I use Adrafinil, which is a non-controlled version of Modafinil. Taking one pill makes me want to do intellectual work and gives me better focus. Taking two pills makes me so sharp I find it a bit difficult to "chill out", so I really feel like spending my energy on working.

The downside is it's difficult to wind down in the evening when I just want to relax, but that's what cannabis is for, I guess.