For Digital Work, I mostly use PhotoShop. Whether I sketch things out traditionally and then scan it in to work on, or draw it directly on screen with the use of a Wacom Intuos 4 wireless tablet. … Though PS is what I use 95% of the time, (mainly because I know it so well) I do have additional digital programs but don’t use them too often, but they can do everything PS does. - The ones I have are; ArtRage, Manga Studio, PaintStorm Studio, etc. There are quite a few digital painting programs out there these days and I find you can pretty much do the same with all of them, but I just find PS to be familiar since it was the one I actually started with for Digital work. … But honestly think having a nice tablet is most important.
And when it comes to tablets, you can’t beat Wacom, mostly their Intuos line. And though I’ve only used 1 of them before, some love their Cintiq line of products, where you draw directly on the screen. A lot of pros use these and they’re really nice, and expensive, but I actually prefer to use a tablet. The biggest thing I find is that working digitally allows one to work faster, but not necessarily better because of all the additional stuff you can do with the digital enhancements. I still basically use it as I would a pencil, but some use all the bells and whistles, filters, etc. to help produce works. 
Here’s one I just did a few weeks ago, just to help get me back into the swing of doing some artwork…
Since then, I’ve been just traditionally sketching with pencil drawings, using my sketchbooks.