I bought one back in Fall last year and its been pretty good. Slightly soft at wide angle, wide open but a when you consider that it was $99US..when I bought it..I couldn't think of any other lens that could beat it bang for buck.
I did a review in it a while back on the DCResource Forum. Here's the link if you like. (
SIGMA 24-135mm Asph. IF - REVIEW! [WARNING, LOTS OF PHOTOS] - Digital Camera Resource Page - Forums) I had noted some inconsistencies on the review regarding my test procedures but they are fairly minor. I volunteer at school and I've used this lens to cover many events before. Especially when carrying multiple lenses is out of the question.
It's pretty sturdy and covers all the commonly used focal lengths. The hood is a great addition.
My only complaints from purchase point up till present is the aperture ring. My copy lost its stop down ability and will only function if on "A" setting. My copy also experiences a menu blanking. Like when you press the "Fn" button to pull up the menu, it disappears in like a second so you gotta press it again. Kinda annoying but I think its only in older lenses. Easily fixable through the warranty Sigma provides although I've yet to take mine to the repair centre.
Otherwise, if you are low on cash, this is a great lens that shuld last you for a long time to come.