My BFF, who ER'd a couple of years before me, sent me a very comprehensive list about handling the transition. Here's an abbreviated version:
1. Develop an exit statement (just don't tell others that's what you
call it). It should be positive (even enthusiastic). It should not knock
your company so you can use it equally internally / externally. It should be
truthful, but it doesn't need to contain all the truth. It should answer
the obvious questions the listener would ask, so that they will congratulate
(not embarrass you to your face or whisper about you behind your back).
Questions people may initially have: whether you were fired, whether you are desperate for your next job, whether you plan to travel / volunteer / relax.
2.Give your exit statement to your boss, desirably as an agreed
follow-up email after s/he gets the resignation news orally and directly
from you. If you are leaving without a severance package, your boss does
not have to agree to your statement, but at a minimum s/he should know that
this is exactly what you plan to tell everyone else, inside and outside the
company. Desirably s/he will also quote your exit statement when describing
your departure to others, so there are no contradictory theories on why
you're leaving.
3.Deliver your exit statement, desirably face-to-face or at least
orally, to as many people as you can. Even a vmail left personally for one
individual at a time, after you tried to phone each one, seems more personal
than a mass-mailed email.
4.Stay on good terms with your boss. In the future, send a birthday
message or service anniversary message or promotion congrats or whatever, so
that s/he still thinks of you positively.
5.Stay on good terms with all possible HR / Payroll / Benefits
people. When one gets tired of you, others will still help you straighten
out your COBRA premium or unpaid vacation days or 401(k) rollover.
6.Shortly before you leave, write every boss that you have ever had,
desirably by snail mail on nice formal stationery. Include your exit
statement and a personal anecdote about some wonderful moment you shared.
Thank him/her amply for all past leadership and guidance (here you can
stretch the truth if you have to).
7.A week before you leave, send tailored email messages in batches to
current colleagues, former colleagues, clients, friends and
relatives. Include an abbreviated version of your exit statement [perhaps
separate your batches between those who already knew you were leaving and
those who will be surprised]. Include future contact information.
8.Celebrate after that last day
9.Don't commit to the first volunteering suggestions, but be open to
all ideas.
She also suggested taking pictures of my desk before the last day (of course, she had a nicely appointed office and I was relegated to a hideous cube for my last year).
I didn't do all of these things but most. YMMV.