The E600 is a budget version of the E620. They are essentially the exact same camera, with some minor features disabled on the E600 in order to drop the selling price. With the E600, they took out the backlit buttons, three art filters, multiple exposure, and aspect ratios.
Bottom line... those things are nice to have, but they aren't worth $100 more. If you are on a tight budget, get the E600. If you don't mind the extra cost, then get the E620.