Thought i would jump in here, Sorry supa but your numbers are wrong. If you are using any of the cannon bodies (except the 5D, 1DS & 1D Which have X1, X1 & X1.3 crop respectively) then the focal length of any lens is multiplied by 1.6. so a 100mm lens becomes a 160mm lens.
And tiny the best advice I have for you is do some reading. http://www.the-digital-picture.com/Canon-Lenses/ the bit that talks about "Canon Lens Recommendations". That link only talks about Canon lens but it still applies to the Sigma & Tamron equivalents.