I used some of the green dissolving tablets, i think they're called Ick Clear, on both of my tanks, tetras and oscars, and knocked it out first time around. I come home the other day, my tetra tank is swamped with it again. I go through two doses of the dissolving tablets, and nothing, crank the heat up, salt, and nothing. I've lost most all of the fish that show the ick at this point.
However, the fish that have been in the tank the longest, and been through the ick once, don't seem to have the white spots anymore, I thought that was pretty interesting.