I've had a big hole in my camera bag for a while, so I'm trying to find the lens to fill the role. I want something that will be my main 'walkabout lens' for the Aussies out there. A lens that can be better than my current Standard Lens I use for waterfall/scenic shots. In addition, I wanted to be able to do some more portrait type pictures of people and my cats.

I am very happy with the two Sigma lenses I bought 2 years ago, a 150mm 2.8 Macro and a 100-300mm f4. My feeling about them has been great build quality, and a performance to cost ratio that fits me. I understand they are only about 85% the lens of a more expensive canon or nikor lens, but they are usually 25% the cost.

So I'm pretty close to buying THIS lens for $400. Anyone else have an opinion on Sigma lenses, or something else that may be good for what I'm looking for but under $600?