Firefox add-ons:
Better Gmail – Compilation of some of the best Greasemonkey scripts for Gmail compiled as a Firefox add-on.
Cookie Swap – Manage multiple Gmail accounts at once with this Firefox add-on.
DragDropUpload – Drop files into attachment boxes easily.
Email This – Emails the current title, highlighted text and link of the active page using email applications like Gmail.
Email Yourself – Use this Firefox add-on to email information about the current webpage to yourself.
GContactSync – Synchronizes the contacts between Gmail and Thundebird.
Gmail Ad Blocker – Removes the ads that are shown in the Gmail interface to make more room for your messages.
Gmail Agenda – Integrates Google Calendar into Gmail.
Gmail Checker – Checks for new emails automatically in Firefox.
Gmail Contact Book – Easily pick contacts when writing mails in Gmail.
Gmail Manager – Manage multiple Gmail accounts and display new mail notifications.
Gmail Notifier – Will monitor a single or multiple Gmail accounts from within Firefox. Displays information such as unread email messages in the status bar.
Gmail Redesigned – A complete new CSS stylesheet for Gmail that changes the look and feel of the website.
Gmail S/Mime – Makes it possible to send and receive signed and encrypted emails in Gmail.
Gmail Signatures – Automatically inserts HTML signatures in Gmail messages based on the address the emails get send from.
Gmail Skins – Change the color of the skin of the Gmail website.
GTD Inbox – Increase the productivity and manageability of Gmail with this Getting Things Done add-on.
Integrated Gmail – Makes it possible to display other Google services like Google Calendar or Reader directly in Gmail.
Bookmarklets:
gCompose – Will display the new mail dialog when pressing the bookmarklet’s button.
Gmail Search Bookmarks – Save searches with this bookmarklet.
Gmail This – Button to email the current page using Gmail.
Multiple Gmail Signatures – Create and use multiple signatures in Gmail.
Greasemonkey:
Always Show CC Field – Will always display the CC and BCC fields in Gmail.
Attachment Reminder – reminds you of an attachment based on words used in the email.
Gmail + Reader Integrator – Integrates Gmail and Google Reader.
Gmail Attachment Icons – Adds bigger and better attachment icons to Gmail
Gmail Emoticons – Adds emoticons to Gmail.
Gmail Filter Assistant – Ads an advanced filter management module to Gmail.
Gmail Macros – Adds extra keyboard shortcuts and macros.
Gmail Persistent Search – Save and access previous searches in Gmail.
Gmail Preview Bubbles – Preview a message without opening it.
Gmail Right-Click – Adds a right-click menu to Gmail to navigate the website faster and more comfortably.
Gmail Spam Count Hide – Hides the spam count in Gmail.
Gmail Super Clean – Provides a cleaner interface for Gmail.
Gmail To – Forces all mailto links to use Gmail.
Gmail Unread Message Count In Favicon – Display the unread message count of your Gmail account in the Gmail favicon.
Google Account Multi-Login – log into multiple accounts at the same time.
One Click Conversations For Gmail – Access conversations with one click.
Desktop Applications:
Blogsigs – For Webmasters: Add the title of your latest blog post in your email signature.
Gdisk (MAC) – Turns the Gmail account into a portable hard drive on the computer.
Gmail Assistant – A notifier for multiple Gmail accounts with many options.
Gmail Backup – Explains how to backup all mails of a Gmail account locally.
Gmail FS (Linux) – Add Gmail as a hard drive in the Linux operating system.
Gmail Mobile – Mobile application for Gmail.
Gmail Todo – Quickly Add ToDo’s to the Gmail account.
GMDesk – Run Gmail, Google Calendar, Google Docs and Google Maps as standalone applications.
Google Email Uploader – Upload emails to Gmail.
Google Mailbox Loader – Import mailboxes into Gmail.
GPhotospace – Use Gmail as a online storage space for your photos.
GSN SMS Notifier – Send SMS when new mail arrives.
GTray – Display notifications of new email messages in the system tray.
KCheckGmail (Linux) – System Tray application for Linux KDE.
Mailstore Home – Backup Your email using this email backup software.
You’ve got Gmail (Trillian) – Adds new mail notifications to Trillian.
Tips:
11 Power Tips For Gmail – A collection of 11 tips for Google Mail.
Add Gmail Tasks To Your Firefox Sidebar – Explains how to add Gmail tasks to the Firefox Sidebar.
Edit Gmail Contacts From Chat List – It is far easier and faster to edit the Gmail contacts from the chat list.
Force Gmail to Always use Secure Connection – Forces Gmail to always use a https connection.
How To Read Mail Without Touching Your Mouse – It is possible to use Gmail without using the mouse at all.
Mark All Unread Mail As Read – Explains how to mark all unread mail in Gmail as read.
Ten Gmail Labs Features You Should Enable – A list of ten experimental features that can be activated in Gmail.
Top 10 Gmail Tips And Hacks – Ten excellent Gmail tips.
Watch Videos right in Gmail Chat – Watch videos that have been posted in Gmail chat in the same window.
What To Do If You Cannot Access Your Gmail Account – A collection of tips that explain what a user can do if he cannot access Gmail anymore.
How To:
Access Gmail From Thunderbird – How to configure Thunderbird to work with Gmail
Access Your Gmail Inbox With Python – How to access the inbox with a python script.
Analyze Mail Usage With Mail Trends – How to analyze mail usage over time.
Archive Mail On The iPhone – Explains how to backup mails on the iPhone.
Attach and Send Any File Type with Gmail – How to send blocked file types with Gmail.
Backup Gmail In Linux – A four step guide on how to backup Gmail in Linux.
Build Advanced Gmail Filters – How to create and use advanced Gmail filters.
Compose Gmail Messages With Launchy – Using the launcher Launchy to compose Gmail messages.
Create A Feed For Unread Gmail Messages – Use RSS Feeds For Unread Messages.
Export And Backup Emails From Outlook To Gmail – How to export email messages from Microsoft Outlook To Gmail.
Fast PDF Viewing in Gmail – How to view PDFs right in the browser.
How To Setup Gmail In External Mail Clients Properly – Explains how to setup Gmail in external mail applications like Mozilla Thunderbird or Microsoft Outlook.
Import Contacts From Hotmail – How to import Hotmail contacts into Gmail.
Import Emails Into Gmail – How to import desktop emails into Gmail.
Manage All Email Accounts With Gmail – Guide for users with multiple email accounts.
Set Gmail As The Default Mail Client – How to set Gmail as the default mail client in Firefox 3.
Send SMS Text Messages – How To send SMS messages with Gmail.
Use Gmail As A Drive In Windows – Configure Gmail to Appear as a normal drive letter in Windows.
Use IMAP in Gmail – Explains how to use Gmail over IMAP.
Work With Attachments – Work with attachments in Gmail.
Misc:
Gmail Mobile - Access Gmail from a mobile phone.
Gmail Productivity Tips – Three productivity tips for Gmail.
Gmail Shortcut List – List of Gmail Shortcuts.
Gmail Shortcuts – How to use shortcuts for Gmail shortcuts.
Gmail Stickers – Get some Gmail stickers for your computer keyboard from Google for the price of a return stamp.
How To Make a Physical Gmail Notifier – Create a new gadget that will tell you if new mail has arrived in the Gmail inbox.