The Tamron 17-35/2.8 is a full-frame lens, the 17-50/2.8 is for cropped sensors only and came out more recently.

For Canon there's both non-stabilized, and VC versions of the 17-50.

My camera has IS in the body and it comes in handy. If you're taking pictures in low light and your subject holds still, you can hand-hold with relatively longer shutter speeds without needing to raise the ISO.

The non-VC is $460 with a $45 rebate so $415. The VC is $650 with a $70 rebate so $580. Or you could try to buy one used.