Here's a handy workout for you guys. You can do it with absolutely NO equipment whatsoever. Basically, stand on one leg and squat down so your butt almost touches the floor (your balancing leg should end up parallel with the floor), still on one leg. Then stand back up while still on the one leg. Do this 10 times and then switch legs for another set of 10. I did just 2 sets of these per leg (20 reps per leg) yesterday and I'm still feeling it pretty badly today. I would highly recommend this routine. It only takes a few minutes too. If you aren't able to balance on one leg, then you could probably do both legs and maybe do 100 or so total to get a similar effect.