Wow some seriously awesome stuff guys!
I haven't had a whole lot of time lately so I try to sketch to and from work.
Paint Tool SAI, it's got a trial period and after that you can purchase it for $50, it's huge in Japan at the moment, everyone is using it, it's a much simpler version of Painter, I really really like it.
OpenCanvas is another great program to try it, it's pretty cheap too with a trial, these two programs also gel well with Photoshop, i.e. taking linework from Sai into photoshop for coloring.