You won't go far wrong with the E05, it has a lot of fans on here. I got one last week and am so impressed with it I have ordered another. There are similar lights with more modes and brighter output, but I personally find them fiddly for keychain use. With the E05 you just twist it on and get a nice beam of light, simple.
The E01 is another good product and cheaper still, but it just seems a bit 'old technology' with its protruding LED and bluish beam. I prefer the cree led and the floody optic on the E05.