I've been experiencing this quite often, and it's quite alarming. Drivers see me coming and don't yield the right of way, probably because they think they can make the turn fast enough and cyclists don't have the same rights as cars. Do you experience this too?
So now I'm very careful at cross streets and intersections. I generally slow down and try to make eye contact, but even when they see me, some drivers pull out anyway. Grrrrh! I'm thinking of getting one of those Airzound horns (although I read they don't last and may not work in cold temps) or use my whistle routinely. Any other tactics?