Since I'm jonesin' to play, I'll start with AIRSOFT! Better than paintball in pretty much any way you can think of.
Keeping in line with hard-core physical activities, I might as well move on to Ninjutsu, the study of which I have been undertaking for nine years now. There's a ninjutsu dojo here at the University of Michigan, headed up by 12th dan Michael Asuncion. We are affiliated with Dr. Hatsumi Masaaki's international Bujinkan Budo Taijutsu organization. For more information on this incredible martial art, check out our dojo homepage, or check out Mats Hjelm's excellent archive of Bujinkan stuff. If you are someone in serious search of an application-oriented martial art, or just a historical or martial arts enthusiast, I strongly recommend going to a dojo and checking it out.
Finally, I enjoy role-playing games of many different varieties. Recently, however, most of my time has been taken up running two ongoing campaigns, one Harn, one Shadowrun. My most recent effort has been the compilation of my omnibus of "house rules" to make Shadowrun more playable.