http://www.exrx.net/Lists/PowerExercises.html
Ok, look at all the exercises under "Plyometrics". Easiest one to do is the Staircase since you only need stairs to be able to do that (you can remove jumping off the box part if you don't have a box). Ideally you can just throw in the Staircase before or after running.
Box Jumps, Stair Jumps, and Broomstick Twist (you can substitute something else for broomstick...like maybe a hockey stick) are all great at increasing strength and adding muscle mass.
You can also do a Jumping Jack-Push Up combo where you do a jumping jack (
http://www.exrx.net/Aerobic/Exercises/JumpingJack.html) and when you come back to the original standing position of jumping jack, you immediately go down and do a push up. Again, this works great because it burns calories (the faster you do the jumping jack the better) and increases strength (from doing the push up).
What you could do is do bunch of staircase or box jumps, find an incline hill and ride your bike all the way to the top as fast as possible, do some jumping jacks-push up combo OR more box jumps, and RUN down the hill with you OFF the bike (and of course, hold the bike in your hands but don't sit and ride it...get the picture?). Do that for a couple of times in a session and see if you can find a way to make it more intensive.
There is definitely tons of stuff you can do to stay in shape. It's just a matter of finding what it is that you wouldn't mind doing.