Cygnus (Cyg)
"The Swan"

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Mythology:  According to the Greek stories, Cygnus and Phaethon were two young men who were good friends.  Phaethon was the son of Apollo, and he asked his father if he could do his job:  drive the Sun chariot across the sky.  Apollo hesitantly agreed, and Phaeton did such a poor job steering the Sun across the sky that it angered Zeus.  Zeus cast Phaethon out of the Sun Chariot, where he fell to Earth and landed in the river Eridanus, a very swift and dangerous river.  Cygnus was saddened by the loss of his dear friend.  Here, the story has two endings.  In the first, Cygnus risks his own life to dive into the river to retrieve his friend's body and give it a proper burial.  In the second, Cygnus wanders up and down the shore of the river singing and mourning.  In either case, the Gods were so moved by Cygnus' dedication to his friend that when he died his body was changed into a swan and placed among the stars.  In fact, the modern expression "swan song" comes from this story -- every time a swan dies Cygnus can be heard singing his sad song.
    A less common, but more parallel to the other classical mythological stories, tale states that Cygnus is actually Zeus himself, disguised as the Swan to fool his wife Hera as he goes to meet or seduce a mortal woman.  Or, Zeus could be flying off to meet the Sea Nymph Nemesis (it is not clear who Zeus is flying off to meet).  If Cygnus (Zeus) was truly flying to meet Nemesis, the result of their rendezvous was an egg (since Zeus had taken the form of a bird), which was placed in the care of Queen Leda of the city-state Sparta.  (The issue is not whether Zeus and Nemesis did indeed have an affair.  What is not clear is if Cygnus -- Zeus -- was flying off to meet her or some other woman.)  The egg hatched a beautiful girl, who grew up to be one of the more famous beautiful women in mythology -- Helen of Troy.
    It doesn't stop there:  In yet another interpretation, Zeus is flying to meet with Leda.  To fool her husband, King Tyndareus, Leda also slept with him after sleeping with Zeus.  Supposedly this let to two eggs, which yielded the twins Castor and Polydeuces (whose name became Pollux in the Roman versions of the story).  This twins are, of course, referred to as Gemini, a constellation of the zodiac.
    It can get even more complicated --  some versions outline the following:  As a result of Zeus' and Leda's rendezvous, Helen and Polydeuces were born; as a result of Leda's and Tyndareus' rendezvous Castor and Clytemnestra were born.  Although it starts to get very intertwined, do note that in this version of the story, one of the Gemini Twins, Polydeuces or Pollux, is immortal, while the other, Castor, is mortal.

Other Interesting Sights:  The large open cluster M39 is in Cygnus at a distance of 800 light years.  But more interesting is the object Cygnus X-1, the first and strongest evidence for a black hole.  Cygnus X-1 is a powerful source of x-rays.  It is theorized that the black hole Cygnus X-1 is pulling matter off a star it orbits, HDE 226868, and the matter heats up as it falls toward the black hole, giving off x-rays.
-Note:  The same stars that give us the constellation Cygnus the Swan also make up the asterism the Northern Cross.
-Interesting Trivia:  The star Albireo literally means "the beak," and Deneb means, well, "rear end of the swan."