Unless you are specifically a BB or training for bulk only, any kind of cross training is good for your fitness and also for small muscles, tendons, etc.
I roller blade. Not only does it do wonders for overall fitness, tendons, etc, but there are things it does for the lower back, abs, calves, and even triceps that I swear I'm not getting from weights alone.
Low intensity long burning exercise seems to help the abs and calves in particular, doing more for me than if I just try to hit them in the gym.
Too much cardio will screw up your lifts though. Groin gets tired from too much blading, then I can't squat for a couple days.