Tamron 17-50mm f/2.8 XR

The Tamron SP AF 17-50mm F/2.8 XS is a great lens with stunning image quality and a fixed aperture at 2.8.

The build quality is very decent, but the lens isn't very light.
2.8 is a large aperture, it is fixed throughout the range, which is great for handheld photos and low light situations. I didn't need image stabilisation (vibration resistance or VR) but there is another copy of the same lens that comes with VR. This aperture gives you the shallow depth of field you need in many photos such as portraits (making the background blurry).

The 2.8 gives a nice bokeh and images are reasonably sharp at this aperture.

The reason I bought this lens is because I wasn't satisfied with the kit lens (18-55) which felt cheap, of bad quality and a narrow aperture. I use the Tamron 17-50mm F/2.8 as a general lens for everyday shooting whether it is portraits, landscape, nature, indoors, weddings, etc.

The lens is an ideal replacement of the kit lens and a very good upgrade for beginners, the image quality is absolutely great and the price is fine.

The range (focal length) is versatile enough for the purposes of standard and everyday shots but doesn't offer much zooming power.

The auto-focus is fast and not very noisy. The zoom ring rotates to the opposite direction of Canon lenses. The lens also comes with a hood.
There is a version of this lens for each of Canon and Nikon cameras.

So, to summarize :
Advantages: Build quality, image quality, wide aperture and price.
Disadvantages: heavy, would be fantastic if the range extended to 70mm.