Crisp citrussy whites and rose (Boschendal Blanc de Noir; ) go well with most seafood, if served with a rich cream sauce then serve with bubbly or a Semillon/Chardonnay blend.
Also think of the weight of the food, if its rich shellfish then pair it with a fuller bodied style white.
Crab: Viognier, Chenin Blanc or Riesling
Lobster/Crayfish: good Chardonnay or bubbly or a buttery rich Chardonnay if served with cream.