Reader Alex writes in with his ubergeeky solution for sending a quick email from his Gmail account—a tiny AutoHotkey application assigned to a hotkey.
Similar to Alex's solution for quickly adding events to Google Calendar, you'll need to add your Google Account credentials to the logon.txt file, launch the AutoHotkey script, and then use the Ctrl+` shortcut key sequence to bring up the quick-send dialog. Since it's written in AutoHotkey, you can customise the script or the shortcut key to something that you prefer, and if you don't want to expose your credentials you can always store the whole thing on an encrypted TrueCrypt partition.
Hit the link for the download, or for more, check out how to send email reminders to yourself with Launchy, use the Caps Lock key for hand-friendly navigation, or add Gmail shortcuts to Outlook with Gmail Keys.
AutoHotKey: command line Gmail AHK script [Just an Asterisk]