Pure cranberry juice. Trader Joe's has a version without added sugar or juice from other fruits. I can't drink this juice straight as it's extremely tart. I take an extremely large amount in water, and then add just a bit to each of the 6-8 glasses of water that we are supposed to be drinking on a daily basis.
I read that the science behind cranberry juice is that something in it prevents the bacteria from being able to cling to the bladder walls.
I swear by this treatment and have never tried the pills. My symptoms rarely last more than a day.
I have heard someone else swear by large doses of grapefruit seed extract. I've never tried it because I know my cure.