I just have to give a shout-out to Maha's. I recently moved back to the Prospect Heights/Park Slope area after being away for 3 years. I was delighted to find this place with its excellent falafel: light, fluffy, delicious balls of goodness dressed in hummus and a cuke/tomato/yogurt mix. Be sure to ask them to add in some of the homemade pickles!
Best of all, Maha, the woman who runs the shop (she also makes the food and works behind the counter every day!), is extremely nice, friendly, and remembers people.