Moving your feet

Can someone suggest some simple (no equipment) drills to improve foot mobility.  This and hands were the biggest problems I've had the last 2 seasons.  My hand placement is getting much better.  I've watched the Centreline football DVD and had the chance to talk to one of the Australian boxing coaches about hand speed and aiming (man that was a sheer luck opportunity) but my problem is I'm planting my feet to try and generate maximum power from the ground up.  As you all know, this doesn't work as soon as the other guy is stronger or faster then you.  

Any suggestions would be appreciated.  Thanks