the tamron 10-24 is about 460 bucks and its a pretty mediocre lens. I'd say save up another 150 and get a tokina 11-16 if you want a really nice UWA lens.
Either get the Tokina 12-24mm f/4 which is about the same price as the Tamron and much better, or pay a little more for a Tokina 11-16mm f/2.8. It has less range but is 1 stop brighter and has slightly better IQ.