SquadMail, now out of private beta, has a brand new Chrome extension to integrate the service directly into Gmail. If you ever feel the need to share email with others but don't want to have to forward to various groups every time, you can just apply a label and let SquadMail handle the rest.
Just install the Chrome extension and load up Gmail to get started. You'll see a SquadMail login option at the top and you can log in using your current Google account. Once you do, it'll walk you through the basics and you can start creating shared labels/folders. Just invite whomever you want to have access to that label/folder and any time you add email to it they'll get a copy (and vice-versa). The Gmail integration works with just about every other feature of SquadMail, too.
You can automatically sync attachments to Dropbox, send email directly to the group through the label/folder's email address and adjust various privacy settings.
If you want to give SquadMail's new extension a try, go grab it for free over at the Chrome Web Store.
SquadMail (Free) [Chrome Web Store]