IntegratedGmail.com

A Firefox Addon that allows you to make the Inbox Collapsible and load your choice of Google Calendar, Reader, Notebook, Groups, Maps, Picasa, Sites, News and Portfolio seamlessly into the gmail interface with the inbox (rather than a separate tab or in the sidebar) using a collapsible box.

It even supports custom URLs (with navigation buttons) and Google Gadgets (including Remember the Milk.) If your are inbox minimalist, you can enable minimalist mode to clean up the inbox even more. Works with Google App Accounts and Gmail Themes.

• “I love this add-on! It saves me tons of time when I can add info from an email to my calendar without switching tabs, or look up a phone number in google voice to send to a friend in a wave. Freakin’ awesome!”
  
• “Probably the best add-on for Gmail. Saves me from always having the calendar open on another tab and now I read my blogs! Support is great…had a problem, Michael emailed immediately and voila…all is good again!!!”
  
• “This is a fantastic add-on that saves me tons of time every day. Our corporate e-mail is hosted on Google Apps and I can’t imagine having to work without this plugin. On top of that, the developer is incredibly helpful and responsive. This is definitely a “must-have” add-on for Gmail users.”