i took a yoga class over the last vacation and it was really cool. felt really stretched and relaxed afterwards, but my muscles still felt like i got a really good workout. and you start small with the poses and work your way up to more advanced ones, so don't be worried about not being flexible enough cause that's the point.
and this may seem weird since you're a guy but dance is actually a really great way to stay in shape too. whether you take ballet or hip hop theres a lot of moving around, stretching and endurance. and its not just for girls, my hip-hop instructor is a skinny white guy. and i'm 80 percent sure he's not gay. although, that's kinda debatable... heheh.