I've been playing with Paint Tool SAI lately, and so far I am loving it. Its a versatile little program that doesn't hog as much memory as PS. Granted, it can't do nearly as much as PS can, but its also not photo software. Its designed to mimic painting. There is a ton to learn about it, but unfortunately there's not a ton of information out there in English about this program. Here's a monochromatic sketch I did with it. I spent a couple hours each night on it for the last couple of nights. I can't wait to dig down deep into this program and see what I can do with it.