Some of the climbs I've really enjoyed the past few years and may do most of them again when the weather gets better:
1) Mount Riga Road ... starts in Salisbury, CT and into MA ... not super steep but goes on for around six miles ... a gravel road that I just love
2) Sunset Rock Road ... also gravel but a harder pack surface than Mt Riga Road but a much steeper grade ... starts in Eastern NY and up into MA. Did a ride last year going up Mt Riga Road, then the pavement descent into Bash Bish Falls (NY) then up Sunset Rock Road ... then, finding my way back to Salisbury.
3) Hope to ride sections of the D2R2 course (Pioneer Vally MA and Southern VT) ... may not ride the organized ride but piece together different sections by myself. Also mostly gravel and relentlessly hilly.
4) If I make it up to Acadia National Park (ME) again, hope to ride the auto road up Cadillac Mountain ... love that ride - gorgeous ocean views!
5) Considering going back out Mount Greylock (MA) ... did it once a few years again but have been thinking about it this winter.

Then, other miscellaneous hills ... can't avoid them in New England.