Bridge to Tomorrowland in the Hub.
Less crowded than on Main Street, but still spectacular viewing can be found near the Hall of Presidents, or deep into Frontierland, past the Country Bears.
(But, from those locations you won't be able to see the spectacular, not-to-be-missed show that is actually projected on the front of the Castle, "Celebrate the Magic," which begins about 15 minutes before the fireworks.)