Hi Mark!
I think Dave is right, the majority of people will still keep the sales letters they have created to themselves for the reason that they have found what has worked in they're market and it works/is working and sharing this with the world will not be in they're interest - this is understandable. But before I continue I will give you one piece of advice I have stuck by "
NEVER COPY AND PASTE!".
You are right that looking at others examples will help you forward, but to put you on the right track.... take an hour out, think about your customers, what they're
thought process is, how to "grab" they're attention amongst the daily onslaught of "junk mail". If one of them is your friend, ask him or her! (getting information from the horse's mouth will help a lot). If you have they're name your already half way in the door.
If you’re just starting with sales letters or your just looking for ideas there is plenty of help ranging from books, audio tapes, online videos, tutorials and I even keep anything I receive through the door that "grabs" my attention. You've already started to move by posting here - and my guess is you've posted in other places too!
All the best
Sam
P.s You will find conflicting information in places, it will be up to you (and your customers) which route you choose - or try both and compare the results 