Tim and Dave offer awesome info on ending the QSO (thanks Dave for explaining the
que-soh sound!

).
I will add, as the HAM radio guru must, that at the end of the LAST transmission the only thing that must be included in the LAST transmission (at any time during the LAST transmission) is the transmitting stations callsign. It doesn't matter about anything else, goodbyes, 73's and 88's, whatever.
When you are not going to transmit on the frequency again as part of the current QSO you must, as part of FCC's part 97 rules which govern the Amateur Radio services, identify the station by voice or CW (or packet, etc) the stations callsign.
Contrary to Daniel's desire

to identify whomever he is speaking to

as well as himself (thanks for falling asleep in my class!) only your own call need be said by you.
Its easy enough to remember--Give
YOUR callsign every ten minutes and during the last transmission (by you).
No amateur operator need give anyone elses callsign as part of their transmission. You are responsible for the correct operation of your own station, not anyone elses. I know it seems hard to grasp, but you may start a transmission by asking if whomever you wish to speak to is out there by their name. Example:
(Once it is determined that the frequency is not in use, or an appropriate time to break in is figured out)
Nathaniel-- Hey perry, this is Nathaniel, you there?
Perry--Yeah this is perry, go ahead nathaniel.
Nathaniel--You got the spare port-a-potty?
Perry--yes I do.
Nathaniel--Thanks. well see you in a few. WØIIN
Perry--yeah, I figure about ten minutes. KDØLDQ
Done. Perfectly acceptable. And in case i didn't hear anything from Perry, i would have just said
WØIIN, clear.
Now, most of us identify more than that, which is more courteous seeing as though we aren't the only people using the frequency. But this is the bare minimum. I suggest somewhere in between. I'll politely tell anyone who I hear doing something that might get someones feathers ruffled.
Helpful?