I would like to write a letter to Brett Favre, the quarterback of the
Green Bay Packers.  What is the address to mail this letter?

Google Answers Researchers are not allowed to post private, personal
addresses, but business contact information for celebrities is
permitted. According to the official Packers website, this is the
address to use in order to send mail to Brett Favre:

Attention: Brett Favre
Green Bay Packers 
P.O. BOX 10628 
Green Bay, WI 54307-0628

"FAN MAIL/AUTOGRAPHS -- 

Where can I send a letter to a player or coach?

Fan mail can be sent to:
Attention: Individual Player/Coach Name
Green Bay Packers
P.O. BOX 10628
Green Bay, WI 54307-0628 

If I send an item to be autographed will be it returned to me?

Autograph requests should be addressed to the individual in question,
should include one item that you would like signed and should include
a self-address stamped envelope (unsealed) so the player can return
the item to you. Do not send items to more than one player in the same
envelope.

Fans would be wise to say 'please' and 'thank you' in their autograph requests. 

Players receive fan mail and autograph requests throughout the year,
but many wait until the offseason to respond. Fans should remember
that players are not obligated to sign or return anything mailed to
them. Also, there is always the chance of items being misplaced, lost
or damaged, so send any/all items at your own risk. Items are not
guaranteed to be returned."

Green Bay Packers FAQ
http://www.packers.com/fans/faq/ 

If you are interested in contacting the Brett Favre Forward Foundation:

"For information regarding the Brett Favre Forward Foundation and
their upcoming events, please contact a representative at
1-800-660-1407 or write:

The Brett Favre Forward Foundation
2300 20th Street
Gulfport, MS  39501"

Brett Favre Foundation Contact Info
http://brettfavre.com/foundation_contact.php

I hope this is helpful. If anything is unclear or incomplete, please
request clarification; I'll be glad to offer further assistance before
you rate my answer.

Best regards,
pinkfreud

The answer was exactly what I was looking for.  There was some extra
infor which I am sure will be helpful also.  Thanks.  It took me a
while to figure out how to get my answer.