Also, and I say this a lot on these forums, but I think the main thing anyone doing any kind of 2D game art should invest in is a Wacom tablet. Their entry-level Bamboo line is very affordable.
Oh yeah, that's being saved up for right now. I definitely need one, because using the mouse is just ridiculously cumbersome!
I think for now I'll stay with GIMP, because with the modifications in that link Kryzon posted, I can have a great palette to work with, which makes it a LOT easier to switch between colors. However, I will check out Spriter, it looks pretty good!
Thanks for the info, everyone!