Recently I've noticed a few guides to the fish you can sustainably eat coming out. There was one for the East coast of Australia recently, though I can't remember the link. This one covers the West coast of the US (via Boing Boing Blog).
Does anyone know of one for those of us eating fish in Europe? Probably be hard to pull together since nearly all fish here is frozen and comes from all over. There seems to be loads of Carribean fish, even. Obviously we must avoid cod, though it may be too late already for them.
One thing I have sworn off recently is scallops. The process of dredging for wild scallops completely destroys the sea floor environment. The farmed variety, like most seafood farming, has major problems with pollution, not to mention the nasty contaminants in the finished product.
It's a tough time to be someone who wants to eat more fish. But there are some things you can do.
Update: Just found this article from The Guardian which seems to supply the info I'm after.