We’ve all had this problem. You try to stick your towel in there. You stake your head and bang it to the side. For hours. But there’s a simple solution:
Hop up and down on one leg, the leg on the same side at which the water is in your ear. The water will simply flow out.
Edit: Herman’s method in the comments also works, counter-intuitively to add a few drops more water, which will cause what’s already in there to flow out.