The Dorian Mode
This scale is the second mode of the major scale. The scale patterns are all exactly the same as the parent major scale, only the second note is now our "home" note - the root and tonal centre of the scale. As a shortcut you can always find this scale by playing a major scale 2 frets lower, but in the long run it's best to think of and learn this as a sound and scale in its own right. It's very widely used to solo over minor 7th and related harmonies, particularly by jazz players. It also works well over dominant 7th chords for a bluesy sound. Download a high-quality, printable PDF here.