These are all good ideas. The one addition I can make is to the "small screwdriver" method. Instead of a screwdriver, I use a cutoff from a cable tie. It's just over 1/4" wide and has enough stiffness to work it under a grip, but it won't scratch the handlebar or tear the grip. The process is to work it under as far as it will go, squirt in some water, work it around side-to-side and forward, give the grip a twist, and repeat. This can also be combined with the "hairdryer/heatgun" method, when necessary. Have fun!
Find an open end wrench that fits snug over the bars. Slide it over the bar and against the edge of the grip and then hammer the grip off hitting the side of the wrench. If you can heat it first in water like Brant suggested it will work even better.
I've also had good success with compressed air under the edge while twisting and pulling.