The Monterey Bay Aquarium has turned its awesome, universally respected Seafood Watch into a free iPhone app. The database, organized regionally, gives a green, yellow, or red sustainability ranking to hundreds of kinds of fish and shellfish -- the West Coast guide rates everything from abalone (U.S. farmed, green) to yellowtail (Japan farmed, red). Click on any fish, and you get a full explanation for the aquarium's rating.
I've printed out and lost my wallet card a dozen times over the years, so now I can finally take full advantage of Seafood Watch. It's one more justification for my outrageous phone bills, too. (Thanks to @cooklocal for the Twitter link -- check the site for Cook Local's review of another iPhone app for locavores.)