Well, if you take a look at the first drawings I posted here, they are done with good old fashioned paper, coloring pencils, markers and water colors
But I'll admit that after getting SAI, I've kind of gotten addicted... >_> It's very easy to learn compared to Photoshop and MUCH cheaper! (tho less features, but you can have Gimp that's free and similar to Photoshop on the side). In addition it's very light-weight, so it works great without lag on less powerful computers.
However, to be able to work intuitively and easily with SAI, you also need a tablet. I first started with a rather cheap Genius MousePen, but it was pretty crappy, really... Wacom's are the best, but they are a little pricey. (I now have a Wacom Intuos 5 Medium, which I absolutely love!) But there's starting to come some good cheaper brands like Monoprice and Huion (or something like that). Medium is the perfect size, no matter brand! Small is just that... too small. And Large is huge, will take up a lot of desk-space and be rather cumbersome.