Summary: I bought this lens because my original Canon lens was broken. For my amateur needs, it is very satisfying. The 1:2.8 aperture is great, and the building seems to be strong. The built-in zoom system is very interesting. The only con is that this lens is heavier than the original Canon. Beside that, no complains at all.
Summary: I agree with some people that this isn't the sharpest lens out there. However, it is a great beginning lens. I have been shooting here, there, and everywhere. I've tried so many unique things with this lens, pushing it to its limit. So far... I'm satisfied. I'm just beginning in the DSLR world with my Canon T2i, but it is not a bad lens for the price. I opted to get this one instead of the kit lens.
Summary: I bought these lens for Canon because kit lens that came with T1i is too bad. What i definitely can say is that replacement worth the price. The quality of images are way better and if you looking for upgrade, then this is probably the best choice. I got the lens in time, and have not found any flaws that were mentioned by some reviewers... may be i am lucky.
Summary: I bought this lens instead of Pentax lens. I use this lens for boyscout activity. The lens is responding quick with auto focus. The picture is good. Specially in the shade I can open the aperture without the flash. I am happy with this lens. I would like to recommend this lens for amateur photographer like me. The price is fantastic. I am happy with this lens.
Summary: I rated 4 stars coz I'll leave the 5 stars to the EX version (EX version is f2.8 at all zoom range better in low lights.) I have always liked the build quality of a sigma lens even for this price once your holding it you can feel that your getting a good quality lens, very solid. if you have extra money I would highly suggest to get the EX version of this. remember that the aperture of this changes as you zoom in.
Summary: I bought this lens to replace a broken Nikon 18-55 kit lens (older, non-VR model). I like the Sigma much better. The faster aperture is great, and it focuses much faster on my D50 (not a camera known for excellent AF). I also like the fact that the zoom and focus are internal - especially important if you use a polarizing filter, the Nikon 18-55 rotates the filter threads when it focuses.
Summary: This is a much better lens than the 18-55 f/3.5 that comes with the T2i /550D. Able to shoot in lower light, very clear photos. I did not purchase the kit lens with the camera and went with the Sigma 18-50mm f/2.8~4.5. Smart move on my part. Great for indoor and outdoor shoots.