Currently working on a crossover piece between Luigi's Mansion and Ghostbusters.
I have roughs done, and I just downloaded Krita, and can't wait to try it.
One of my friends recommended it, and it looks pretty comprehensive.
I wish Paint Tool Sai was available on Mac, because it's what I'm most used to, but who knows, maybe Krita will be just as good. Or, maybe I'll do it as a comprehensive vector again.