I "discovered" an Osprey Aether 30 pack this weekend and couldn't resist. From what I can find it is a smaller version of the Aether 45, but is unlike the other packs in the series. It has a roll top and mesh side pockets, a web on the front for compression/gear hauling, and a sleeve between the back panel and the pack body for a hydration bladder. It has a padded back and shoulder straps, a sternum strap and and unpadded hip belt.
At first look, I thought it was a waterproof design. The roll top will help keep water from entering the top, but all the seams are untaped. It does make for a simple and strong closure that is resistant to dust and moisture and can be adjusted for volume. I would use a liner for wet weather.
I was looking for a light and simple day pack in the 30L range. I do like side pockets for water bottles-- I don't like stashing bladders in the same compartment with electronics and cameras. Osprey should have put some grommets in the bottom of the hydration sleeve in case it gathers rainwater or has a reservoir leak. It is not a SUL pack at 29oz, but I can live with that for a day pack.
Another roll top pack that has caught my eye of late is the Outdoor Research Drycomp Ridge Sack that is a 16.4oz, 34L waterproof pack with a big front pocket. I've been waiting to catch the bargain on one.
Another OR roll-top is the Dry Peak Bagger. It is 27L and only 9.2oz. I think those who like the old GoLite Ion would see the potential in this one. I want one with side pockets, but it does have a big pocket on the front with a sleeve for an ice axe. MSRP is just $55. It's a winner if it isn't too uncomfortable.