YelpMix MySpace-style social networking with Zagat-style reviews and a dollop of the Yellow Pages, and you get Yelp. Yelpers log on to the site to write reviews of their favorite - and least favorite - haunts, such as restaurants, bars, and dry cleaners. You'll go in looking for a restaurant tip but end up sticking around to meet some like-minded neighbors. The three-year-old company is the brainchild of co-founders Jeremy Stoppelman and Russel Simmons (in the white shirt), both of whom earned their Silicon Valley cred as star engineers at PayPal. --O.R.