If you have the driveway for it, our experience is that rollerblades, while not a perfect substitute for ice time, are good for balance, agility, and power. And it is fairly easy to find used rollerblades in good condition (may just need new wheels) so you don't have to spend a fortune. Our kids have spent hours in the driveway on rollerblades with a net, cheap street hockey sticks, and green biscuits.