Help me oh wise photography people, please, help. I'd like to have a new lens for shooting agility/dogs in action shots, and I went ahead and in a spur of the moment bought a 75-300mm lens that mom bought me and as much as I appreciate the lens, it's not exactly the quality I want. She paid $130 for it brand new, I believe. Anywho, I'm kind of looking at selling that one and getting a different one, and I'd like to not have to pay as much as my car for it, so I've been scoping out some "cheaper" lenses that still, to me, look like they might be decent. So far I've found these ones: Canon EF 55-200mm f/4.5-5.6 II USM Telephoto Lens for Canon EOS SLR Cameras - $300 http://www.amazon.com/Canon-55-200mm-4-5-5-6-Telephoto-Cameras/dp/B0000CCW64 Canon EF 28-105mm f/3.5-4.5 II USM Standard Zoom Lens for Canon SLR Cameras - $270 http://www.amazon.com/Canon-28-105mm-3-5-4-5-Standard-Cameras/dp/B00004YZQ8 Canon EF-S 18-200mm f/3.5-5.6 IS Standard Zoom Lens for Canon DSLR Cameras - $550 http://www.amazon.com/Canon-18-200mm-3-5-5-6-Standard-Lens/dp/B001ET6QFY Tamron AF 70-300mm f/4.0-5.6 Di LD Macro Zoom Lens for Canon Digital SLR Cameras - $160 http://www.amazon.com/Tamron-70-300mm-4-0-5-6-Digital-Cameras/dp/B000EXOXVA http://www.ebay.ca/itm/Tamron-70-30...74263754?pt=Camera_Lenses&hash=item20c0d6eaca - $220 package Tamron AF 70-300mm f/4.0-5.6 SP Di VC USD XLD for Canon Digital SLR Cameras - $400 http://www.amazon.com/Tamron-70-300mm-4-0-5-6-Digital-Cameras/dp/B003YH9DZ4 And of course, some of them are a bit higher than I'd like to pay, but I was just wondering if anyone could give some input on all, or any, of these lenses. I'm shooting with a Canon Rebel xSi right now, and that's not likely to change for a year or two, so... thoughts, opinions, ideas? Thanks!