I use a bell. It's cheery and more likely to be heard than me trying to shout something at some poor pedestrian. I could care less if people think it's dorky.

Once in a while you get people who act like they don't realize you're ringing that bell AT THEM or who slow and look around as if they've never heard such a thing before. For the former, I will THEN call out "passing on your left!". For the latter, I just shout "Bicycle!" and smile at them and ring the bell more as I go by.