Light incline BB presses. Ditto DB presses and DB flyes. I also like cable flyes from the bottom - squeeze your upper inner pecs at the top and hold it.
I focusses specifically on bringing up my upper chest about a year ago and found dropping from 275 on the incline for like 6 to about 185 for 12 (light, 4 second negative and a quick 1-2 second positive). I also threw in 3 sets of light DB incline presses 3 days later (REALLY light just to get blood into the upper chest to help healing). I did that for 4-6 weeks straight, gave my chest a break for a month and hten did something similar but with slightly different exercises and order thereof.
The trick is to really focus on using your upper chest to fight the resistance of the weight. This will work if you take 4-5 months and really concentrate on it. Worked for me anyways and I don't think I'm special.