Watch the Open-D Tuning Piece: Key of D online guitar lesson by Vicki Genfan from Acoustic Rhythm Guitar Cookbook
Listen to the basic version in standard tuning. I think you'll find that open D is a really fun tuning to add to your toolkit. The notes I tune to are these (starting with the 6th or lowest string): D A D F# A D.
For both studies, you'll hear lot's of color tones. In the first study, we'll work with a fingerpicking style referred to as Travis picking (after Merle Travis), and in the 2nd study we'll work with some harmonics.