1. make some sort of pesto with herbs ( I like cilantro, mint & basil), garlic & olive oil. Puree in the food processor & smear al over fish.
2. super easy when I'm in a hurry--1/2 mayo & 1/2 dijon mustard (better if you have a flavored dijon like one with lemon zest). That's all! sounds wierd but is great.
3. Sake, soy sauce, brown sugar, ginger, garlic, rice vinegar.
Just remember when you marinate fish, not to do it for very long (about 1/2 hour or so) or the marinade will start to "cook" the fish & it will be mushy or overdone.