SeafoodWatch already has a pretty solid iPhone and Android app that does this[1], but I'm all for more options and having raw JSON available.
[1] http://www.montereybayaquarium.org/cr/SeafoodWatch/web/sfw_i...
[1] http://www.montereybayaquarium.org/cr/SeafoodWatch/web/sfw_i...
http://www.edf.org/page.cfm?tagID=1540 (eco best / worst)
http://www.edf.org/page.cfm?tagID=17694 (health best / worst)
You can even get a pocket guide that goes into your wallet that you can take out whenever you go into a sushi restaurant or fish market. Here in NYC there are a lot of hedge fund managers with serious neurological problems from eating sushi every day for years. They manage billions of dollars in assets but their hands twitch like they have parkinsons.