You could easily check out Newport, RI for 36 hours.

www.gonewport.com

Also, you could head up early to boston, and explore the city....you'd squeeze alot more out of your 36 hours by alreeady being up there. You could take a train up from Providence and you wouldn't need to rent a car....(oops, just saw that you've already traveled to Boston.)

I'd suggest Newport also (rather than spending too much of your 36 hours driving to and from your destination). What are your dates in August? Do be aware that the Jazz Festival in Newport will kick off on Friday, August 8, with an evening concert at the International Tennis Hall of Fame...followed by two full days of jazz on three stages at Fort Adams State Park on August 9 and 10.

Definitely second the suggestion of Newport or Cape Cod (I'd stay closer to the canal end of the Cape just to limit the driving).

Don't try to go to MV or Nantucket as you won't have enough time. You'd eat up a lot of time if you tried to go to VT or ME driving. The distances don't look too bad but the traffic will make it slower since people do return home on Sundays after going for weekend trips.

If you decide on Newport, book now or soon. You may not be able to get a place in Newport (depending on when you want stay) so this may influence you to going to Cape Cod instead. In Newport it is hard to get accommodations without notice.