Mike P.T. said:
Dumbell bench presses and incline dumbell bench presses or even decline dumbells. I too have hurt my right shoulder years ago and even though it's healed 100% now, I still got niggling pains every time I did it. So I needed to find an alternative. I found dumbells allowed a great alternative and I actually find it a superior mass building movement overall. It allows for a fuller range of motion and also works your stablilizing muscles more due to you having to balance each arm. You also aren't restricted in terms of motion in a sense that each arm on a barbell bench press for example is somewhat on a fixed plan of movement unlike the dumbell which allows you to lower and raise it more freely in a manner that should not aggravate the shoulder even further.
If the problem persists though you might want to lighten the weight and/or back off from training chest as much too. I know it's hard huh. BUT.. it's like taking one step back, then 2 steps forward.
Supplement-wise msm and glucosamine may help. I never tried either but heard they work well. Going the anabolic route Deca(which I have tried for problems and it worked like a charm!!!) or G.H. can help too although G.H. is more costly and some note that it gives them even more problems with there joints.
Lastly if it is that bad or gets worse go see a doctor. Better safe than sorry. Good luck bro.