[Stache]

Since I grew up and live in NY and really started skiing in the late '60s I'll start there:
Big Rock Candy Mountain (outside Troy)
Easton Valley (kinda other side of Willard)
Petersburg Pass
Alpine Meadows (Saratoga)
Hickory Hill (Warrensburg)
Dynamite Hill (Chestertown still open)
North Creek Snow Bowl (~original Gore)
Big Tupper
Mt. Whitney Club Lake Placid '88-'89 the year I taught at Whiteface
Eagle Mt.
Shoemaker Mt. (Not on NELSAP list but seen from Thruway I-90 west of Fonda/Fultonville)
Scotch Valley
Highmount
Nevele - Resort near Ellenville - Not on NELSAP list, resort is open but I don't think they ski anymore. EDIT - I just searched and found their golf site, called and confirmed they do still ski there in the winter.

Massaschusetts
Brodie (Jiminy was/is a ski area with a bar, Brodie was the BAR with the ski area out back)
Jug End

CT-
Powder Ridge - I remember their radio commercial from the snowless winter of '79-'80 or '80-'81 a little boy asking his father "Daddy, What's snow?" Dad replies "Well son, Snow is this white stuff that falls out of the sky." Son asks "You mean like a DC-10?"

Vermont
Prospect Mountain (had a ~40M? ski jump)
Dutch Hill
Haystack & Corinthia (which one had the tunnel to get from the main mt back to the base of the beginner slopes?)
Magic (When Simon Oren ran it)
Maple Valley (won Gold in a CDSC race there)

Boy do I wish I had saved a brochue/trail mapo from all of them.

Note to self and daughter: Take an extra brochure and trail map from every ski area you visit and keep them, and your lift ticket in a scrap book or other safe place. Forty years from now you will be glad you did.