This year is the 400th anniversary of the exploration of the Hudson River by Henry Hudson, so instead of taking place on the East River, like every year, the fireworks will be on the Hudson River (West Side -- between Manhattan and NJ). The previous years, people went to Brooklyn to see the show, but this year the best views will be from Manhattan's West Side between 23rd and 59th Streets and along the New Jersey waterfront (Hoboken, Jersey City, Weehawken...).
Unfortunately, it gets very crowded, so you should arrive very early (by 6 / 7 pm if you want a good view!)

On this page, you can read more information about the 4th of July fireworks: http://manhattan.about.com/od/eventsandattractions/a/nycjulyfourth.htm

If you are willing to pay, there are other options:

• Empire state building ($125/person) -- Need to book very early
• Cruise on the Hudson River: The Waterway http://www.nywaterway.com/Home/TakeaTour/PurchaseTickets/4thofJulyOption... or Circle Line
• Bars with rooftop: Hudson Terrace, 230 5th, Hudson Sky Terrace, W Hotel in Hoboken, Plunge, etc.

These last 3 options are definitely the best but you should book early and be ready to spend a few $$...

Happy 4th of July and have fun!