http://www.klymit.com/splash-25.htmlThis one has ten reviews and five star average:
https://www.thenorthface.com/shop/waterproof-daypackThat said, I personally use zip-loc bags and a rain cover for my favorite backpack or day pack and that works fine.
Unless I'm transporting by water, I rarely use a "waterproof" pack, and even then, I usually use a waterproof duffel to transport, then switch to a best fitting, best purpose pack with a cover.