How much do you want to spend?
Do you want to rock the dorm, or listen quietly while you study?
How much space do you have? The desktop speakers take up a little space, but do you have room for a subwoofer under the desk? It makes a BIG difference.
The only compatability problem is, believe it or not, with other Apple speakers. Apple put out some digital speakers that you would need an adaptor for. Other than that, you plug the speakers into the headphone port, which is a mini stereo jack. Standard stuff.
With a name like amusicguy, I'm guessing you are interested in quality sound. You need to hear the speakers before you buy them. Go to Best Buy, or Fry's, or some place like it that has many different speakers set up for you to listen to. Choose, and then go to the web to get the good price.