[ajross]

Depends entirely on what you want to do in "meatspace", of course. There are lots of options for, say, robot control out there. Hacking one's Roomba seems popular. If you have a spare laptop or netbook, there are huge numbers of USB-based interface devices you can use to deal with the outside world without even leaving the comfort of your PC.

And, when you're ready for "serious" work (something other than turning lights and motors on and reading sensors at 10 Hz), you'll probably want to be looking at FPGA development boards and learning Verilog or VHDL. Take a look at the products from http://knjn.com for example.