My daughter has a Sigma 10-20mm f/4-5.6 EX DC AF HSM SLR lens. She got it for her Canon Rebel XSI, but it works with other brands like Sigma and Nikon. She has used it less than ten times, but more than five. It comes with the case.
She wants $350 FIRM. It sells new for near $500 to over that depending on where you buy it.
Here is one on ebay for example
Thanks for looking