Control Option Command

A big pet peeve of mine is that unlike most other apps Mail.app is a goddamn hassle to just quickly switch to.
If you’ve closed the window in Mail rather than just hidden or minimized it, it seems to be no way to make it reappear with a keystroke. Instead you have to actually move your mouse to the dock and click the icon. Unacceptable.
The solution? Open your system preferences and navigate to the Keyboard Shortcuts tab under “Keyboard & Mouse”. Scroll to the bottom and make a new entry for Mail.app and create a shortcut for the Menu item “Message Viewer”. Map it to the keystroke you’d like (I chose ⌘-O) and you’re set to go.

The cool thing is that you can pretty much create shortcuts for any menu item in any app. In theory.
Sadly it doesn’t consistently work in all apps, as I’ve outlined once here, and of course it only works for menu items, so for more specialized stuff you’ll have to use more advanced alternatives such as QuicKeys, which I gave a short introduction to here.