I will freely admit, that I have probably one of the worse roll casts around. It's pretty much a downright disgrace. Every now and then I try to improve it, but no such luck to date.
Tonight was another night of perusing videos in an attempt to not suck at this any more, and I found a video by Mel Krieger, one of the best casting guys to hold a fly rod. It was his video that really made the connection for me on how to haul, so hopefully this will help with my rolls as well.
If your roll cast could use some improvement, here's the video.