The Entertainment Software Rating Board has published a free iPhone app that allows content-conscious shoppers to search out ratings and content descriptions while they're in line wondering if Left 4 Dead 2 is appropriate for little Billy's stocking.
The ESRB's entire ratings database is searchable, with full certificates available for titles back to July 1, 2008. Said the ESRB president Patricia Vance: "This new rating search app puts all this information at parents' fingertips when they need it most, right at the store. It's a powerful tool that will help assure parents that the games they give as gifts are not only fun but also appropriate for their children."
Not sure how frequently it updates; for the core, I guess it's another way to spy on what's been approved, and spoilers in games we know are in the pipeline. You can grab it here (link will open iTunes.)
The app launched with the following PSA. I would have loved it if she read off the ratings summary for BioShock 2 instead.
ESRB Launches iPhone Ratings App [Game Politics]