bent over laterals (with arms bent) will hit your rhomboids well. don't be to concerned with weight with these, just get your elbows as far back as you can.
they sit in under your traps so hit'em hard first.
shrugs (with a grip that's just outside shoulder width) & medium grip upright rows also do a good job on the top & middle traps which help dramatically in upper back thickness.
mine respond well when i pull explosively & hold for a second at the top. do these heavy though.
i also found pullovers or straight arm pulldowns (shoulder width) help build the teres muscles on the upper, outer part of the back. they look pretty impressive when fully developed.