I know Maglite has a terrible beam quality and is usually hated here. But....I still have several AA Maglites and I figure I might as well make it as good as possible. Is the Opalec LED conversion unit a good aftermarket product?
http://www.all-maglite-4-less.com/detail_mag_ledmod.html
http://www.all-maglite-4-less.com/detail_mag_ledmod.html