Let's see... you need something valuable that can be easily tracked. Hmmm, let me think, let me think....
What're you, retarded or something? Ever hear of a CELLULAR PHONE?! Dude, you can go buy a $60 pre-paid Boost Mobile phone, which comes with (drumroll please...) GPS tracking!
Let it get stolen, then report it stolen to Nextel. Make sure to keep all the long ass ID numbers and shit off the phone for reporting it. OR, if you don't want to go through that hassle, have a look at mologogo.com, which allows you to register, download their software, and track the GPS-enabled phones of other members (for free, I think, but I haven't registered so I dunno... Looks like it's free of charge). So, just register your $60 pre-paid phone with mologogo, let it get stolen, then go online to mologogo.com and track the motherfucker! You could also download Google Earth, so that you can see satellite images of the coordinates where your cell phone is currently located. I mean, c'mon, a pre-paid cell phone is the perfect target for a thief. You have no real "claim" to it since ownership is anonymous, so anybody could just steal it and use it, no problem. Your thief will probably even take it home with him and then you can Google-Earth right in on his fucking house and go pay him a visit.
Am I a genius? Well, yes, but for this I didn't need to be. I just used GOOGLE, you dork. Now, certainly there are less expensive ways to do this. You could build a miniature transmitter and then use 3 recievers to triangulate its location. Ham Radio operators call this "fox hunting" and it's sort of a sport among Hams. However, it requires a more in-depth knowledge of electronics and radio communications then I believe you have. So shell out the cash for a pre-paid cell and bust this motherfucker. Make sure you talk to your school's administration and let them in on what you're doing. That way, they'll know the phone is yours when you try to get it back from the thief.
And, above all, don't blame me if this doesn't work. If you shell out $60 for a Boost phone and you never see the fucker again, it's not my fault. Still though, I wish you luck and hope that you DO nail that sonofabitch.