Tokina 11-16 has a fast 2.8 max aperture, but not sure what good that would do a person that is buying wide angle primarily for landscapes and such, which are usually shot stopped down. I had that lens for a brief period and although I had a bad copy, it was okay- just too restrictive in the focal range for my taste. It's almost more like a prime with wiggle room than a zoom. I'd prefer something like a 12-24/4. I would gladly give up 2mm on the freaky distorted wide end, compared to say a 10-20, to gain 4mm at the long end. I had the Sigma 10-20 for my Pentax kit for quite a while and loved it. I just found in reviewing my shots that hardly any were under 12mm and that I recall many times wishing I could go at least a little bit longer. But that's just me.

I've heard good things about Canon's 10-22, so that's another one to consider depending on which brand you go with. But if you are in Canada and want to buy in Canada, I doubt any of those lenses could be found new for under $600. I am not familiar at all with the Tamron you mentioned. The Tokina 12-24 might be right around that price. The Sigma is more like $650 and the Tokina 11-16/2.8 is $750. All the OEM lenses will be well over that: Nikon 10-24 or 12-24/4, Pentax 12-24/4, Canon 10-22, etc