I'm currently using the Sigma 70-300 APO DG
as this came out best within my budget (over the similar priced Canon/Tamron equivalents) in the many reviews I read when deciding which lens to buy for my 300D. The lens suffers, like most at this price ($250-$300), from softness at full zoom, but other than that, I'm more than pleased. The DG
lenses do not have the compatabilty issues that affected earlier Sigma models and I've had no problems with any of its functions.