Here's a little background, as these charts won't include every fish under the sun: When it comes to mercury in fish, the name of the game is biomagnification. What's that? It's the process by which large, predatory fish accumulate higher levels of toxins because they sit higher up the food chain. Mercury enters the ocean's food chain via algae and plankton, but these plants don't accumulate that much mercury. Biomagnification starts with the small fish who feed on the algae/plankton - all of the mercury that was previously 'spread out' amongst a lot of algae now concentrates in the fish who eat them. This process continues further and further up the food chain, with larger and larger fish accumulating larger and larger amounts of mercury, like a pyramid. While we're at it, here's an graphic that demonstrates biomagnification.
This image explains how DDT accumulates in sea birds, but you get the point.
On to the fish. Here's a great image from the National Resource Defense Council.
It's big, to be sure, but it's very thorough. This chart is the source document from which a lot of other guidelines are written, so I recommend keeping this handy. (The '*' symbol means that there's significant pressure on wild populations due to fishing, and the '**' symbol is to call your attention to the fact that farm-raised salmon, unlike wild salmon, may contain PCBs and other chemicals.)
The second is from the great state of Vermont, and was published by a collaborative effort between the Department of Environmental Conservation, the Department of Fish & Wildlife, and the Department of Health. I especially like this one because it includes information on fish that you might catch in lakes and rivers. While it's specific to Vermont, the information on this chart is likely applicable in other states as well.
I hope this guides you on your way, and remember, if you don't see the fish you're eating on these charts, you can still estimate its mercury content by thinking about it's feeding patterns - the higher it is on the food chain, the more mercury (and other toxins) you're dealing with. Have a great week and eat well!