I am in love with Ina Gardner's method.
You take half of the volume of chocolate you wsh to melt. microwave for 30 seconds then stir. let stand for 10 seconds. microwave again for 30 seconds on 50% power. then mix in the other half of the volume of chocolate. instant tempering and you don't have to worry about gritty chocolate.

Either a double-boiler or the microwave on 50% power have worked for me. Just stir periodically, and remove from the heat before the chocolate has completely melted. This way your chocolate should remain tempered (which is nice depending on what you're using it for.)

Here's a video we did about melting chocolate: http://www.food52.com/blog/1912_how_to_melt_chocolate