I'm sure most if not all of the list I'll put in has been said but here goes.

1: Compressed air
2: Small flathead screwdriver and any lubricant, i.e. soapy water, windex etc, I personally tend to use a disinfectant as to clean my bars as well.
3: Heat! A warm day or a blow dryer, and you can begin twisting the grip at one end moving your way along until it begins to spin freely and will pull off.
4: This ones drastic, get a knife and begin slicing open the grips along the seam or make your own seam cutting.