I had a Sigma 70-200 HSM II - was a very good lens and I was very happy with it

I think I sold it for £365 on this forum and it was in very good condition with no marks on it at all. The only reason I sold it was to get the optical stabilized version which is much better but much pricier (one sold here the other day for £500 which was a bargain)
As mentioned above - make sure you get the HSM version as you need the built in AF motor for your body.
I've also heard of complaints about the Tamron AF system - best avoided I think if you can.
Keep looking and one will turn up - heres a bit of history on the Sigma ones :-
70-200mm F2.8 EX APO - Original version, minimum focus distance 1.8m (1999)
70-200mm F2.8 EX DG - Adds 'digitally optimized' lens coatings to reduce flare (2005)
70-200mm F2.8 EX DG Macro (HSM) - Minimum focus distance reduced to 1m (2006)
70-200mm F2.8 EX DG Macro HSM II - Improved optical performance (2007)
70-200mm F2.8 EX DG OS - Optical Stabilizer added and complete redesign (2010)
Hope that helps a little
