I just bought a Giant Escape City, so that's what I would recommend if you have a good bike shop nearby that sells Giant. All of the big name brands have hybrids, so test ride as many as you can and get the one that makes you smile the most. $600 is plenty for a hybrid.

People seem to eschew fenders, but I highly recommend them. It's fun to be the only biker you see without a giant brown stain all over your back, neck and hair.