Well Sigma and Tamron will be where it's at for you then.
I think I'm correct in saying that the 300D, like my old D30, won't accept "digital only" lenses (The kit lens from my 30D doesn't fit it!) so beware of that if this IS the case.
I was intending to try to go for a straight upgrade to the kit lens for the 30D, but have now realised that there's not really the "right" lens in the area for me. (Partly because of wanting to be able to use all my kit on both bodies, so EF-S and DC lenses are out). I'm now looking towards teaming up a Sigma 24-70mm f2.8 with a Sigma 12-24mm to get the coverage at the lower end. Trying to find something nice and fast at the 18 - 70mm area seems tricky to me.