My old Sigma tele-zoom lens is pretty useless nowadays, particularly in cold (the mechanism gets stuck, and you cannot zoom even by using force). I went shopping, and got a Canon EF 70-200 mm L — my very first L class lens. This is the cheapest of line, and does not have an image stabilizer, for example. But it should produce much better images than my old one, the aperture should be enough for daylight at least, and the usability is a huge upgrade to my old Sigma. A review is here: http://www.the-digital-picture.com/Reviews/Canon-EF-70-200mm-f-4.0-L-USM-Lens-Review.aspx.