the salmon served at dinner at Be Our Guest is outstanding. (no salmon there at lunch)
Also the salmon served at dinner at Rose & Crown is very good (they don't serve it at lunch)
also the salmon served at yak & yeti is very good
for quick service, the salmon at sunshine seasons in epcot is very good.
i only order salmon, so i have a lot of experience with it at WDW...
i'll look at my list and let you know where else you can get it..
it's pretty good everywhere in WDW that i've had it.
be careful when you plan, as some of the restaurants only serve salmon at lunch or dinner, but not both. Though some do offer it at both.
and this changes, as they change their menus - so you have to check.