What % of the moon can be seen from earth?

The "near side" of the moon always faces Earth, because the moon's rotation is locked to its orbital motion around the Earth. So the quick answer is "50%."

In reality, I seem to recall that it's a little more than 50% owing to some east-west wobble as seen from the Earth.

Sorry, no sources -- I'll defer to others for an authoritative answer.

Surprisingly more than a little...

Q5. What percentage of the Moon's surface is visible from the Earth?

A5. 59% due to a phenomenon called libration. (The Moon's orbit is not a perfect circle, so at some points in its orbit, it is turned slightly eastward, and at other points it is turned slightly westward, allowing us to see more than 50% of its surface from the Earth.)

http://home.adelphia.net/~chassler/trivia_quiz100.html

Thanks to decal, and armed with the word libration, I found a couple of other sites:
Stargazing.net gives a full explanation; and here is a striking animation clearing showing the wobble (which is both longitudinal as well as lateral).