If you're willing to install a Google Chrome extension and share a link to it on Twitter or Facebook, there's "Old Compose".
From Lifehacker:
Finally, a fix for those of us who aren't fans of the redesigned Gmail compose window. The Old Compose extension brings back the old, familiar interface Google left behind.
Once installed (reboot Chrome after dragging the add-on to the extensions page), Old Compose works seamlessly in the background. That is, hit the compose button (the "c" keyboard shortcut) and the old message window you know and love is back. That means you'll get a wider compose area automatically (pop-out window still available), one-click access to add Cc and Bcc recipients, more formatting options at a glance, and so on.
Old Compose is free, but it requires you to share the link on Twitter or Facebook before you get the download. For some of us, getting the old Gmail back is more than worth it.
