I think the problem many people have is not utilizing their chest and isolating those muscle. Instead, people rely on shoulders to get them through a chest workout. This only leads to injury. Flys are generally one of the best things you can dor for your chest and there are several variations (bench, cable, machine).
One exercise I do that really isolates the chest is as follows:
standing, take 3 ten pound plates and place them sandwiched between your flat palms.
Hold the plates together at chest level, just below your nipples.
Keeping your shoulders back and relaxed, push your arms forward, keeping the plates held together and your palms pushing together flat.
Extend your arms as far as you can without using your shoulders and then back to your start position.
You will feel a good burn in your chest.