First of all, remove the puller, and make sure that the washer, if any, is removed from the base of the crank. Usually the washer ID is too small for the pusher, and so has the pusher doing isometrics until it breaks.

Then, here's a trick I use with super tight cranks -- those that feel like the pusher will break before they come off. Assemble the pusher, and tighten as far as you feel is possible. Now, take a hammer, and give the end of the pusher a solid shot. There's backlash in the thread, and the hammer will drive the pusher forward a fraction of a millimeter, which is usually enough to do the trick.

Otherwise there's the old Murphy's Law standby. Remount the other crank and tighten. Replace the bolt on the right side, but back it off about 1mm. Go for a ride and look for the steepest hill you can find and attack it in too big a gear, standing on the pedals. nine out of 10 times, you'll hear or feel a click as the cranks pops loose (be sure the bolt is there so it can't come off completely).

For the one out of 10 times that this trick fails, repeat it out in the boondocks, on a road with little or no traffic. Do not bring tools or a cell phone. Better yet do this late in the day, with an approaching storm. I absolutely guaranty you'll be walking home with the crank off.