Tennis racquet - recommendations?

Though I am startlingly unathletic, I have decided to learn to play tennis. Can anyone recommend a good beginners' racquet (i.e. <$100) or give pointers on things I should look for when purchasing one? Any good sources for gently used, secondhand equipment?

Go to Paragon (Union Sq). They will help you.

The right size is important. You need to measure the size of your grip which will tell you what diameter the handle should be.