I have a Ryobi cordless electric mower that has served me well for the past eight years and is still going strong. Unfortunately, they don't make it anymore, but here's another option: the Neuton. It provides only a 14" cut rather than the 18" that my mower has, but it has several desirable features that my mower doesn't have, such as an available extra lift-out battery.
Either mower (as well as a corded electric mower) will pollute significantly less than a gas mower does. Mowing with a gas mower for an hour produces the same amount of pollution as driving a car 50 miles.