This is a really good marinade for salmon from Fine Cooking—I cooked the salmon on the stove but it would be great grilled. This makes ~3 cups, enough to marinate 3 lb. food. You can also use it for steak, pork, chicken, or vegetables (especially mushrooms and potatoes). I halved this recipe for four salmon steaks.
1 8-oz. jar Dijon mustard
1/2 cup grainy mustard
1/4 cup Honeycup mustard (or you can use any honey mustard)
1 cup white wine
4 oz. (1/2 cup) unsalted butter
4 or 5 scallions, trimmed, white and green parts chopped
Fine sea salt and coarsely ground black pepper

In a medium bowl, whisk together the Dijon, grainy mustard, Honeycup mustard, and white wine.

Melt the butter in a 3-quart nonreactive saucepan over low heat. Whisk in the mustard mixture, scallions, 1 tsp. salt, and 1/2 tsp. pepper and heat, whisking, until the sauce has emulsified. Cool completely before using. The marinade will keep, tightly covered, in the refrigerator for up to 2 days.