POur compléter ce que dit Zuk :

Canon 15 85 : Canon EF-S 15-85mm f/3.5-5.6 USM IS - Review / Lens Test Report - Sample Images & Verdict
Tamron 17 50 VC : Tamron AF 17-50mm f/2.8 SP XR Di II LD Aspherical [IF] VC (Canon) - Review / Test Report - Sample Images & Verdict
Tamron 17 50 NON VC : Tamron AF 17-50mm f/2.8 SP XR Di II LD Aspherical [IF] (Canon) - Review / Test Report - Sample Images & Verdict