Mail

1. Contacts / Groups
2. General Settings Highlights
   • Conversation View / Threaded Messages (disable / enable)
   • Signature & Picture
   • Vacation Responder
   • Send & Archive
   • Undo Send
3. Reply "More" Options
   • Mark as Unread
4. Labels
   • Create
   • Manage
5. Filtering
6. Labs
   • Canned Responses
   • Signature Tweaks - Puts your signature, at the bottom of your message - NOT the whole message (including quoted messages)
   • Undo Send
   • Customize Keyboard Shortcuts
   • Multiple Inboxes
7. Gmail Offline
8. Themes
9. More Tab in a Message
   • Adding Tasks
   • Create an Event
   • Create a Document* (includes the body of the message)
10. Chat, Video Chat, Instant Messages
11. Desktop Notifications
12. Sign out Remotely

Chrome Browser

• Offline Gmail
• Multiple Accounts

Other Resources

• Mail in Google Apps (A Complete Guide)
• Google Mail Official Blog

Chrome Extensions

• All Gmail Extensions
• Right in Box - Tracking, scheduling emails, and adding reminders.
• Streak - Let’s you schedule e-mail, track projects, share types of e-mail for others.
• Rapportive - Adds information about the sender or sendee of an e-mail
• Any.Do - Add the Android / iOS / Chrome / Web-based to do list to your Chrome Browser.
• WiseStamp - Multiple signatures, connect to social networking, etc.