I’m a huge fan of Gmail. I’ve been using it for years, and have converted several small businesses over to Google Apps so they can take advantage of it. I find it fast and flexible, and can get to my seven years worth of email from any computer on the planet.
For the last few weeks I’ve been extending Gmail’s functionality with a Firefox extension called “Xoopit for Gmail“. Xoopit makes Gmail more social, and gives flexible access to attachments others have sent me.