It is no secret that when I lived and worked in Mexico, I ate everything off the street. I grew to appreciate and love street food and never got sick…ever. The trick is to find vendors who are popular with the locals.
This website http://www.streetfood.org/ is all about Consumers International (CI) campaign for safe access to street food and to preserve street food life. If you find any others, send them my way.
San Francisco had a Street Food Festival this year. Check it out http://sfstreetfoodfest.com/
Here is the list of Food Vendors using Twitter: http://www.seriouseats.com/2009/05/a-list-of-street-food-vendors-trucks-carts-using-twitter.html
Some more websites on street food are:
http://www.foodreference.com/frvideos/html/street-food.html
http://www.forbestraveler.com/food-drink/best-street-food-story.html