Wide lens advice!

I have the 60D with the EF-S 15-85, the EF 50mm 1.8 and a Tamron EF mount 30-300 DI VC.  I would still love to get the 10-22 but the only reason I would not buy the canon is it's an EF-S lens and I can see that one day I will upgrade to a full frame camera.  (15mm on a 1.6 crop is the equivalent of 24mm on a full frame camera)

My brother in law has the Tokina on his Nikon and loves it.

If you don't plan on going full frame in future then I would go the Canon route.  The 24-105 is also a fantastic Lens from what I understand and one that would support you for years to come.

Just my $0.02

Trevor.