Hi adrian
i think that you hit the nail on the head with your question "What species are attracted by them?"
a flasher is
anything that you dangle in the water to attract fish's attention, to bring them within your range, and hopefully keep them there for long enough to get a shot at them.
as far as what species are attracted to them, i have had a lot of interest from all sorts of fish. Batfish and old woman angle fish circle it, biting the shiny stuff, and kingfish shoot in and buzz around it. you also attract the unwanted interest of the toothy, ten-gill variery :blackeye.
as far as ideas for what to use as a flasher go, here are a few options.
the silver bag from box-wine, cut into strips.
perspex mirrors, glued back to back and sealed with nail varnish
stainless steel plates.
fising lures like plastic squid skirts
christmas decorations
cd's but not cd-r's.
this list is what i have used. there are some other good ideas out there, so keep asking.
remember that you'll need a float and line to attach the flasher to. you also need a weight to keep it down. if you plan to swim when the flasher is deployed, the weight needs to be quite bit because the drag on the line pulls the flasher up and behind you. by big, i'm talking 200-300grams.
when using one, just jig it up and down so that it looks alive, and remember bot to stare at you flasher, mesmerised by the bright coulours, but to keep looking around for the fish that you are after.
cheers and good luck.
mark