Quick - how about this:

Sharp, solid, value.

I keep meaning to try the Tokina 11-16 but the Sigma's range and performance are impressive, especially considering the price. Mine is sharp enough pretty much across the range although to be frank I don't pixel peep at extreme corners.

Colour and contrast are brilliant and it's built like a little tank.

Apparently sample variation is the only real problem with these lenses.

This one, Nikon 18-70, and 70-300VR with a 50mm 1.8 work great for me.