As of right now I'm only using sketchbook express for digital drawing. Any suggestions for software?
Hard one. Most artists I know use Photoshop exclusively, especially since it became more affordable. $2000 in one go was never an option for me, but since they've gone to a more affordable $20 per month, I've been very happy to deliver part of my pay-cheque to the Adobe office every month. (I actually pay 50 a month to get all their programs, since I use more than just Photoshop).
But that's coming from someone who's been using the program for more than a decade for everything from photo editing to webdesign to concept art and texture maps.
So, honestly, I would refer to
this message board, and more specifically,
these subforums.
ConceptArt.org hosts some of the premier artists in the digital world, and though they're a bit snobbish and elite every now and then, they're pretty dang smart and helpful enough if they notice you're keen to learn.