While Yelp, Yahoo Local, Zagat, Michelin and others can provide a fairly clear picture of whether or not an eatery is worth going to, there's another resource called CleanScores that takes a scientific approach--health inspection scores. Since scores are public, CleanScores takes that data along with a track record of all infractions, and turns them into an eye-friendly, searchable database. While only good for San Francisco and Los Angeles residents at the moment, the site is eventually planning to expand out to other parts of the United States.
What makes the service really useful (besides finding out your favorite sandwich shop has a rat problem), is that you can get a snapshot of its inspection history that, in most cases, goes back for years. This lets you see if an establishment has mended its ways after doing poorly, or is continuing on a downhill slope of culinary catastrophe like some of the places you see in Kitchen Nightmares.
In addition to the search, which lets you find any place you're looking for, the site keeps a best and worst section that compiles the last three scores of some of the top- and bottom-ranked restaurants. It also has a feature called Sparklines that averages the last five inspections and puts them into a color and size-coded bar with a numerical value. In many cases, some of the infractions won't churn your stomach, but there are others that might make you think twice about going to that local eatery.
To help promote ratings found on CleanScores, its creators have a promotional emblem that lets top-rated restaurants put on the front of their establishments the likes of any other of the award logos you tend to see from popular review services. Each emblem is only good for three months--just in case anything has changed, so people can be guaranteed the score is up to date. Going forward, I'd like to see the service partner with some user-generated sites like Yelp and Yahoo Local to add an extra layer of usefulness, since knowing how good a place's French toast is can sometimes be just as important as knowing if it might be coming with a side of cockroaches.