Do chest butterflies for, well, the chest.

Incline/olympic/decline bench presses also help out the chest a lot. Rotate if you can. Try working the shoulders as well, as that'll make your chest exercises that much easier. Also, a spotter will do
wonders; definitely will help you reach your potential. Try to get more protein in your diet if you want to bulk up.
Back exercises, hmm... I did a lot of back extensions using weights. Try using some 15's or 25's and work your way up to 50's. I also did a lot of barbell upright rows. Those are a little more difficult and focus on the shoulder a bit more - but there's definitely some back muscle being put to use if you do it right.
I loved hitting those higher weight marks that give you a sense of accomplishment. There's nothing quite like it.