Watch the Slippers online guitar lesson by Joe Dalton from 50 Acoustic Blues Licks You MUST Know
Here’s another drop D lick. Listen to Greg Jennings from Restless Heart on "Victim of the Game" for more of this kind of stuff. This is a great way to set the mood of a minor blues piece. Another song to listen to is from the Charlie Daniels Band. I think it's called "Long Haired Country Boy". The song is in D major, but they use a lick like this.