Google is your friend
but every letter of notice I have sent has:

* been dated on the day I handed it in
* been to the point (i.e. "I hereby give [your notice period] weeks/months notice of my resignation
* had a brief explanation (i.e. "I'm leaving to pursue another great opportunity" ... but you don't need to say where)
* included a final closing thank you (i.e. I wish the firm and my colleagues all the best for the future)

erm... that's about it

HR won't give a monkey's if it's a big firm, if it's a small place they might appreciate a wordier thank you.
( chart cat has an itch, Mon 27 Apr 2009, 10:17, Reply)