It's called "Cool Wall," and you can get it over at Apple's iTunes store. Looks like TG may have released the app before it was finished cooking, however: it's $1.99 and so far, the reviews are mixed, with purchasers complaining about things like cropped pictures of cars. The app page claims updates are on the way, but buyer beware in the meantime. Thanks for the tip, Bryan!
[Source: Top Gear via iTunes]