I just did the Traveler loop last week. My favorite loop in the Northeast so far, and when I say Northeast I mean NY, NH, VT, ME, QC, NB, NS and Nfdl all at once! And yes, I'm including Katahdin... Let's talk about a not-yet-known summit (I should have done it before, in bushwack-era).
Other "less known" jewels (but internet could change that in a near future):
Jay range and Nundagao (NY), Hunger-Worcester (VT, well known locally only), Boundary Bald (ME, approach is dull but beautiful ridge walk), Doubletop indeed, Collins-Mattawee (Quebec, favorite spot of the guy who hiked from Florida to Gaspesia via the AT and IAT, then came back!), Jacques-Cartier-Xalibu traverse (Qc, Gaspesia), Groulx mtns (Qc, a remote 4 day backpack though, but what a backpack!).
On the usual lists but underated:
Goose Eye (as SK mentioned before), Grace (aka East Dix), Saddleback-The Horn, The Nubble, Santanoni in winter when there's enough snow to be higher than the scrub and get a long and beautifully open ridge walk.