I use a golite vo24. Yes, it's a bit large for trail running, but it is one of the few that are available in sizes. It snugs down well and weighs 24oz. Some people complained about the bottle pockets being too small, but I use a bladder. Also the hip belt pockets are much larger than my gregory z30.

No internal frame so I can roll it up and stuff it in a larger bp for dayhikes.