Like tnflyfisher said, yellow is good pretty much from now until fall. Yellow Stimulator, Mr. Rapidan, Yellow Sally, and Neversink Caddis are all pretty good bets. Green Weenies and even Pink Weenies can be productive as a dropper, especially at the higher elevations. And I've always had good luck with bushy Wulff style flies like a Thunderhead or Irresistible or even a Royal Wulff. Throw in a couple of Haystacks and some EHCs in various colors and you'd have a real good start for the mountains.
Fly fishing - it's cheaper than a bass boat!