I just found this posted on MFP:
Stand-up.
Put your feet like this: | | in front of you at shoulders' width apart. Go up on your toes then back down. Spend about one half second on the ascent AND one half second on the descent. Do this 25x.*
Stretch for a few seconds, then reposition your feet like this: \ / with toes pointed outward (about 45ยบ). Do another 25 reps.
Last step is to point toes inward like this: / \ and do the final 25.
*You can steady yourself with a finger on the wall if need be. If you're not feeling a burn by the end of that, I'll be shocked.
(Learned this from a guy who used to be a boxer. It's meant to create definition without the bulk.)