We have good bells on all our bikes and use them consistently. If I think the person may not have caught on to the bell sound, I will also use my voice. If it's not a cyclist, I'll say, "I'm passing on your left" or "Bike coming up behind you on your left" or something like that. I feel pretty strongly about giving path users good warning. Although the cyclist we passed Sunday who was fiddling with his damn Ipod seriously pissed me off when he got startled, after we'd rung our bell. Jerk.