Managing multiple Gmail accounts

Discovered MailPlane (Mac OS X only) today that lets you easily switch between multiple Gmail accounts and see the number of new emails at a glance. It works by overlaying desktop functionality on top of the embedded WebKit/Safari core. For example, you can drag and drop photos, auto resize photo prior to sending, and copy/paste images directly as attachments.

It's not free or open source but overall feels like a high quality app. The time saved in attaching images/files alone is worth the (current price) of $25, and it's a must have for people who use multiple gmail accounts.