Cygnus

From the Wikipedia entry on the constellation Cygnus, the Northern Cross, one of the easiest to find this time of year:

The constellation also contains the X-ray source Cygnus X-1, which is now known to be caused by a black hole accreting matter in a binary star system. The system is located close to the star Eta Cygni on star charts.

Eta Cygni is in the long part of the neck of Cygnus, about halfway from the wings to the head. Cygnus X1 isn't visible to the naked eye, though, and Eta Cygni is very faint.

Beta Cygni is Albireo, a double star, at the swan's head. Alpha Cygni, the tail, is the brightest star, named Deneb.

Cygnus contains several variable stars too, as this website describes.