MCW has a pretty decent-sized fitness center in its basement...free weights, home gyms, and aerobic exercise equipment (treadmills, stairclimbers, ellipticals, etc). I hope I'll be motivated enough to hit it up once in a while come next fall.
As far as I can tell, the University of Wisconsin med school doesn't have a separate fitness center, but your ID will get you in any of the university's 3 large recreational facilities. I would imagine most other state schools are like this.
My med school is still building the fitness center. It is going to have a basket ball court weights and cardio equiptment. I think it is a necessary part of medical school to burn off stress and maintian health... we are trying to be leaders.
If your school doesn't have one, take that up with the student union. Maybe talk to a local gym about group membership?
Our school has one with weights/cardio. They are also supposedly opening a new one in July or August in the New Dorms. School has a wellness program. The new gym and dorm also is supposed to have a new daycare center.