A long time ago Sigma made an EX series 15-30mm f/3.5-4.5 Zoom lens, it is a surprisingly useful focal length range on both FX and DX sensors. My copy performs remarkably well at 15mm, image quality decreases at the long end though.
It will be very interesting to see how the new Tamron lens performs - it is aimed squarely at people looking for a cheaper alternative to the Nikkor 14-24mm f/2.8G, or camera systems that do not have such a lens in their current full format line up.
Pentax K5IIS - Sigma 15-30mm f/3.5-4.5 EX DG @ 15mm f/8 1/30th ISO 80
At 15mm image quality is virtually indistinguishable from my Sigma 8-16mm at the same focal length. Though at 30mm end of its range this lens is inferior to the Sigma 18-35mm f/1.8 Art and the Pentax FA31 Limited.