Watch the 9th Chords online guitar lesson by Stu Hamm from Stu Hamm U: Fretboard Fitness
Another way to add spice and flavor to your chordal playing is to add different notes other than the root, 3rd, 5th or 7th to add more tension. Here we add a 9th (an octave 2nd) to major and minor chords. The minor 9th is especially haunting, as you get a nice ½ step between the 9th and minor 10th. I've gotten a lot of mileage out of these voicings and I hope that you will as well.