Good tip, ReefSkunk. Compound butters are more or less the tried and true flavoring for grilled fish at restaurants, and they taste good in all kinds of stuff.

If you really like salmon (don't try to mask the flavor so you like it), salt, pepper, and a mixture of minced garlic and peanut oil (or other, flavorful oil with a high smoke point) is about as good as it gets. This is how I usually eat chinook.

I usually like to add a few, subtle flavors to coho. Seasoned the same way, with a citrus butter or similar at the end is usually good. I also like it with a puttanesca sauce over the top, but I like all those briney, Mediterranean flavors; your mileage may vary.

The best coho I ever cooked was an accident I haven't been able to recreate since. Basically, I made a butter with herbes de Provence, garlic, shallots, and lemon zest. The plan was to baste the fish after flipping, and put some more butter over the top while plating. I got distracted while cooking, and i left the grill unattended for a few minutes. When I came back, there was a small fire in the grill. After a few, choice explitives, i opened the lid and blew out the flames. The fish had a beautiful, brown crust on the flesh side. A little more butter, on to the plate, and BAM!, a delicate, salty crunch, immediately followed by a veritable explosion of buttery, herby omega 3, with just enough twang from the lemon zest to complete the trifecta. It was awesome. I'm not sure i'll ever find the right balance between searing and on fire to recreate the magic again, but I can tell you that even without the crunch, that recipe is a winner. It's even better with chanterelles sauteed in pinot noir and finished with some of the butter. Drink the rest of the pinot noir for additional euphoria.