Same as HeffeD, PDF-XChange Viewer is almost as light as Foxit [which has had it's own fair share of mild controversy over installing toolbars, etc.], which I've also used and a credit should be given to its lightness and speed. I also use NitroPDF Professional, which is pretty good, but getting too close for comfort to Adobe. Tried Nitro PDF Reader for a while, it just felt a bit "middle of the road"...