I assume we're talking about an alloy wheel which has fused itself to the drum. I've run into this problem many times, especially at the beginning of every winter when removing summer tires.
I use the spare tire as a sledgehammer. Hold it vertically and swing it at the stuck wheel, giving it alternating smacks at the 3 o'clock and 9 o'clock positions. It may take quite a few blows, but this should eventually break it free. Plus, you have little to no chance of damaging your alloy wheel since you're using a big piece of rubber to hit it.