Here’s a list of the Extensions I use:

All-in-One Gestures
This extension allows you to execute common commands using mouse gestures, rocker navigation, scroll wheel navigation and page scrolling.

Answers
Alt+click on any word or term for quick info (Definitions, up-to-the-minute reference, and more). No selection necessary

Better Gmail
A compilation of the best Greasemonkey Gmail enhancements in one extension.

ColorZilla
Advanced Eyedropper, ColorPicker, Page Zoomer and other colorful goodies

Copy Plain Text
Copies text without formatting

CountdownClock
Displayes a clock that counts down to a target date.

CustomizeGoogle
Enhance Google search results and remove ads and spam.

CuteMenus - Crystal SVG
Adds icons to all menus.

Flash Switcher
Switch between various Flash plugins or remove current plugin

Forecastfox
Get international weather forecasts and display it in any toolbar or statusbar with this highly customizable extension.

FoxClocks
Displays local times around the world in the statusbar/toolbar.

Get directions from Google Maps
Select addresses on a web page, right click the mouse, and choose “Locate on Google Map” menu item, to see the location at Google Maps and find the directions.

Gmail Notifier
A notifier for Gmail accounts.

Gmail Skins
Skins and other extra features for Gmail.

Google Calendar Notifier
This extension provides robust notifications and display of your Google Calendars for today, as well as showing any upcoming all day events for tomorrow.

Google Notebook
Allows notetaking while browsing.

Google Toolbar for Firefox
Take the power of Google with you anywhere on the Web!

Html Validator
Adds HTML validation to the View Page Source of the browser. The validation is done by Tidy from W3C.

IE View Lite
Cut down version of IE View.

MeasureIt
Draw out a ruler to get the pixel width and height of any elements on a webpage.

MR Tech Local Install
Local Install power tools for all users.

PermaTabs
Create permanent tabs that don’t close, and stick around between sessions.

QuickJava
Allaws quick enable and disable of Java and Javascript from statusbar.

TargetAlert
Provides visual cues for the destinations of hyperlinks.

Toolbar Buttons
Adds toolbar buttons

ViewSourceWith
View page source with external application

Web Developer
Adds a menu and toolbar with various web developer tools.