I also like rear delt crossovers - aka reverse cable crossovers. Set up the cable machine like ur gonna do cable cross overs for pecs, except take the left cable grip in your right hand, right grip in your left hand and go from them crossed in front of your face to a pull back in the same way that you would on the pec deck machine for rear delts. I keep the weights low because it gets hard to pull and keep your arms out and in tight form but it gives you a killer squeeze at the end of the pull. And of course, a controlled return back to the startign position. Remember to keep your chest out and form tight.