Hi Andrew! I'm Scott, one of the teachers for the class.
I use the Arduino Uno in class. You can get one at most Radio Shack stores in town, or from Micro Center, or from any number of web sources. The current version is the Uno R3, but it doesn't matter if you happen to get an R1 -- the differences are minor. Some students have brought the Arduino Mega 2560, which is fine too.
The ones not to get:
- Any of the little ones (Nano, Fio). They're hard to work with.
- Arduino Ethernet. It needs a special cable to connect to the computer.