I ended up buying the Canon 10-22 which is awesome although a bit more expensive ... you could always sell you D7000 and come over from the dark side
I've only heard good things about the sigma, & I think you'll find the Tokina is 12-24 ... an the extra 2mm at the wide end make a HUGE difference - I looked at the sigma 12-24 full frame & decided against it.
Have a look at
www.slrgear.com and/or
www.photozone.de