There are many manufacturers out there - as to which one is 'good', i really don't know.. you'll have to wait for some of the guys who actually use 'em to tell you.
BTW - i have seen at canadian distributers that little screw in replacement back for mag lights as well - it's a pressure switch, and the cord attaches to your pump so that when you grip it the light goes on (or off if you don't touch the pressure switch). They don't interfere with the natural stroke of the pump. I think they're about 20 bucks. I always thought that made a lot of sense.