I did some "neo-soul" stuff a while back, and if you listen to it, it's the voicings of the chords (as well as the extensions and alterations) that give it that phat, full sound. There are loads of voicings, rootless, 3-7, quartal, many more, hit up google, it's mostly experimenting though. Once you know what notes you want to play, find a good order. Although a good rule of thumb is to include the 3rd and 7th in your left hand, (the 5th doesn't do much, but provides more sound, so to speak), and then try adding extensions to spice it up in your right. To maj7th chords, adding 9ths, 13ths, or a flat5, usually works. For minor7th, try 9ths, and 11ths. For dominant 7ths, you can add the 9th, 11th, or 13th, as well as a flat5, sharp5, flat9, sharp9, or sharp11. All the above extensions and alterations do not alter the nature of the chords.
Also I use quartal voicings a lot for horns, for example, trumpet : Bb, alto sax: F, tenor sax: C, trombone: G. I think they sound good, you can use the same idea for strings. Just look at a chart for the circle of fifths and you can see where I get those from.