Swimming is good, but don't expose yourself to the excess pathogens and caustic chemicals of a public pool if you can avoid it.

Lifting weights is also good.

Cycling can be good but one must really know what he's doing, and go easy on the prostate pressure!

Yoga has done wonders for me. The stretching, at least as much as the exercise factor, helps clear my lymph system, and my body in general, of crap that builds up....