Amazon Links:
E-Mail: A Write It Well Guide--How to Write and Manage E-Mail in the Workplace
http://www.amazon.com/E-Mail-Write-Guide-How-Manage-Workplace/dp/096374559X/ref=sr_1_1?ie=UTF8&s=books&qid=1225772357&sr=1-1
Just Memos
http://www.amazon.com/Just-Memos-Legal-Research-Writing/dp/0735562326/ref=sr_1_1?ie=UTF8&s=books&qid=1225772439&sr=1-1

Blog:
Email Overloaded
http://email-overloaded.com/

Discussion Forum:
EmailDiscussions.com
http://www.emaildiscussions.com/

Educational Sites:.edu
Writing Effective E-Mail: Top 10 Tips
http://jerz.setonhill.edu/writing/e-text/e-mail.htm 
Memo Writing
http://owl.english.purdue.edu/owl/resource/590/01/

General Sites:.com
A Beginner's Guide to Effective Email
http://webfoot.com/advice/email.top.php
Email etiquette
http://www.emailreplies.com/
Eliston Word Processing Plus
http://www.elistonwordpro.ca/id19.html

Newsletter:
The E-Marketing Maven
http://www.envoynews.com/envoy/index000035379.cfm

Peer-Reviewed Journal:
Business Communication Quarterly
http://bcq.sagepub.com/

Wikipedia Definitions:E-Mail & Memo
http://en.wikipedia.org/wiki/E-mail
http://en.wikipedia.org/wiki/Memorandum

Link Exchange:
Dan's Mail Format Site
http://mailformat.dan.info/