I am writing a heartfelt resignation letter to a staff I love dearly. 
We have grown so much and achieved so much over the last year.  I
would like a couple of quotes that allude to growing as a team; no one
can take away the experiences we've had; or despite my absence, their
efforts and achievements can continue etc.  Anything along those
lines...

I like this quote about teamwork, from U.S. Supreme Court Justice
Sandra Day O'Connor:
 
"We don't accomplish anything in this world alone, and whatever
happens is the result of the whole tapestry of one's life and all the
weavings of individual threads from one to another that creates
something."

And this one, from the great football coach Vince Lombardi:

"Individual commitment to a group effort -- that is what makes a team
work, a company work, a society work, a civilization work."

And this, from industrial tycoon Henry Ford:

"Coming together is a beginning, staying together is progress, and
working together is success."

Here's a bit of wisdom from Tom Wilson's comic strip "Ziggy":

"Many of us are more capable than some of us - but none of us is as
capable as all of us."

My favorite farewell quote comes from an anonymous source:

"You never leave someone behind; you take a part of them with you and
leave a part of yourself behind."

Do any of these grab you?

I was thinking of quotes similar to the last one.  I love the quotes
about teamwork but I'm not sure they could be incorporated into a
resignation letter, which is the umbrella I wanted them to fall under.
 More background info is that I initially started the position when
things were going horribly.  We started from the bottom and worked our
way up - so I want to say something that expresses my faith for them
as a team...moving forward.  That we have grown together, and they
will all still continue growing and will continue to use the tools
they have developed.  I realize a quote cannot be that specific...but
that is more the tone.  They have left a mark on me and I have left a
mark on them.

What about something along these lines... 
(sourced from: http://www.stevemoore.addr.com/quotes3.html)


"What lies behind us and what lies before us are tiny matters compared
to what lies within us." ---  Ralph Waldo Emerson

"Your chances in any undertaking can always be measured by your belief
in yourself." --- Robert Collier

"The greatest glory in living lies not in never falling, but in rising
every time we fall." --- Nelson Mandela

"Even if you're on the right track, you'll get run over if you just
sit there." --- Will Rogers

"Being yourself is not remaining what you were, or being satisfied
with what you are. It is the point of departure." --- Sydney Harris

"We are what we repeatedly do. Excellence, then, is not an act, but a
habit." --- Aristotle

yes, those are great.  Please post as answer!

I'm more than happy to help out, but I'm not a Google Researcher so I
can't post the answer (but, gosh, I'm thrilled to be asked!) Wait and
see what the researchers come up with. You will probably get the
perfect quote!

I saw this on the wall of a faculty room at a local school. No
author's name was mentioned. It's probably a bit verbose for the
purpose that you describe, but it might be appropriate.

"Great team work is like a great work of music. All the voices and
instruments may be singing and playing at once but they aren?t
competing. Individually the instruments and voices make different
sounds, play different notes, pause at different times, yet they blend
together to create a whole new sound. This is synergy."