My favorite urban legend has to be either Bloody Mary. Not the actual Elizabeth Bathory, but the legend about looking in a mirror and saying her name 3 times and all the terrible things that happen to you. When I was a kid, my babysitter's daughter told me about it. We tried it then, but it was daylight out, and so she convinced me that it didn't work then, but at night. I remember that night, I wouldn't walk down the hall because there was a mirror on the outside of the bathroom door. When I finally had to, I ran past it, with all the lights on, of course. I think the next day I had actually forgotten all about it, lol. :P
I can't recall the name, but those in the know about Urban Legends will probably know the story. There was this rocking chair (in a museum now) that was in a pub, and it was the favorite chair of this guy, and when he died he cursed the chair - and since that time, anyone who sits in it, dies shortly afterward, even if they don't know about the legend. This is such a problem that it's actually mounted high off the floor in said museum in England.