The California Grill in the Contemporary Hotel is great, they pipe in the firework music for Magic Kingdom and you can also watcg the fireworks from their viewing platform outside - take something warm to wear though as it gets quite breezy as you're really high up.

In Epcot you get a great view of the fireworks from the Rose and Crown in England - you will need a table outside and try and eat about an hour before the fireworks so you can get a good table.