I've been looking for a good sunscreen too. I asked about it on these threads a while ago so maybe there might be a suggestion in there that might help.
Here's the link http://www.acne.org/messageboard/index.php/topic/319240-have-you-found-a-sunscreen-that-doesnt-break-you-out/
and while I was trying to find my thread I found another http://www.acne.org/messageboard/index.php/topic/316553-looking-for-a-good-sunscreen/
there are probably more so just do a search on the forums to see if you can find any that help you 
Hopefully some others can add some more suggestions here though.
Clinique CityBlock SPF 40 is far superior to any other I've used. You can also get it in SPF 25. It's formulated for oily skin and is fragrance free. I'm not sure whether it could be labelled non-comedogenic, but it does not break me out, and most reviews online say it doesn't break them out.
Neutrogena Ultra Sheer Sunblock only contains helioplex, which is a chemical block, and you need to apply any sunscreen with a chemical block at least every 2 hours if you live in a sunny and hot climate, every 4 hours if live in a temperate climate. I hope you were re-applying it throughout the day, otherwise a chemical block is useless unfortunately.
Look for a sunblock with a 'physical' block - i.e. either titanium dioxide or zinc oxide, only these two will give you thorough protection throughout the day without having to re-apply often. A physical block will last at least 6 hours, unless you get yourself wet or you sweat a lot. I live in the UK so I can get away with only applying CityBlock once a day, in the morning. Clinique CityBlock contains titanium dioxide which I prefer to zinc oxide, because in my opinion it applies more easily and is longer lasting, but it's personal preference, zinc oxide is just as good at being a sunblock.
Unfortunately this product is a bit pricey at 17, but one 40ml tube lasts ages.
