GMail Documentation

Google Apps documentation for Gmail—

• http://learn.googleapps.com/
• Official Gmail Blog (handy for news & updates on features), http://gmailblog.blogspot.com/

Also—

• Gmail Essential Training, http://www.lynda.com/Gmail-training/Essential-Training/77961-2.html
• Gmail for Power Users, http://www.lynda.com/Gmail-tutorials/for-Power-Users/84524-2.html
• Lynda.com (via www.LearnIt.ucla.edu for UCLA associates) has many more Google specific modules