Hi, I was browsing the net looking for reviews etc on the canon lens and came across this site. Sorry if this topic has been discussed already, but as I said I am new to here! I have a canon rebel XSI for the body, and just bought the kit lens and one other to start with, but having my camera only 6 months I am already wanting more out of a lens! I do outdoor sports / pets / portraits. I like what I read on the 70-200mm F/4L but unsure if I would need to upgrade in cost to the IS or if I could go with the non IS. Any suggestions would be appreciated, as I said I am mostly outdoors in good lighting, would like to focus on portraits and outdoor sports (horseback riding to be specific)