Luckily, Snopes is divided up into different topics and sub-topics so that you can zoom in on something manageable. Possible topics might include urban legends about love (or about weddings), horror stories, college life, stories about medicine (or pregnancy in particular), legends about food, crime stories, animals, and more!
You can also search Snopes for a specific word or phrase using the search engine at their site. So, for example, here is a search of the site for the word football.
To get an idea of some of the specific types of urban legends that students have worked with in the past, you might want to take a look at some of these past Storybooks.
There are other urban legend sources that you can use online, but I would strongly recommend that you focus on Snopes.com because of the extremely helpful background material that they provide for each legend. You can learn a lot from reading the history of each legend, and that in turn will help you in writing your own author's note for each story.