Harrison Schmitt saying "Okay. I'm going to get the Pro. (Pause) 99 Proceeded 3, 2, 1...Ignition"
Immediately after liftoff, Gene Cernan added "We're on our way, Houston!"
http://www.hq.nasa.gov/office/pao/History/alsj/a17/a17.html
Click on "Return to Orbit" under "Completing the Mission" and scroll to time stamp 188:01:32
The oft repeated fallacy that it was Cernan saying "Let's get this mother out of here" is discussed in the above link as well, right below that time stamp.
The last words spoken while standing on the surface were from Gene Cernan: "And, as we leave the Moon at Taurus- Littrow, we leave as we came and, God willing, as we shall return, with peace and hope for all mankind. "Godspeed the crew of Apollo 17"
The next words were "Bob, I am up on the ladder and I'm going to be going through the hatch"
Reference: Same link as above, click on "Close-out" under "The Third EVA" and scroll to timestamp 170:41:00
The last words spoken while the lunar module hatch was still open were the stunningly dramatic "Close the hatch"
by Harrison Schmitt, followed by "Hatch is closed, let's see if I can lock it" by Cernan. 170:44:44
