Expanding the 3pi
There's only so much you can do with the 3pi on its own, but with a little soldering you can make it do much more. If you've never soldered before, it's inexpensive and easy to learn. This is an excellent page, complete with videos, for those wanting to pick it up. Desoldering is an equally valuable skill that is sometimes necessary as well.
If you've never soldered anything, you'll want to practice before you start attempting to expand your 3pi! Having never soldered before, I was ready to work on my 3pi after practicing with twenty or so diodes on a blank PCB, even with my incredibly unsteady hands. Of course, for each person this will vary, so exercise some common sense. For each practice joint that you solder, you'll get better.
Wired Serial Comm.: Requires soldering six joints onto the programmer and two on the 3pi. A good choice for competent beginners.