The used Tamron 17-50mm f2.8 Di-II LD SP AF mentioned yesterday is long gone, but the new condition is available for a reasonable price for an f2.8 APS-C zoom lens, $300 gets you this lens in the four SLR systems (Canon, Nikon, Pentax Sony Alpha Minolta Dyxum Maxxum Kraxum). At Adorama you have a choice of 4% promotional rewards or free lens-y accessories, while at B&H Photo you get 4% promotional rewards. These are new condition with a 6-year Tamron USA warranty.
NOTE: this is the older non-VC (non-stabilized) version.
PS: this is blog-certified to be Tamron, not Tokina 🙂