Next lens - wide angle considerations

[BIGEYE]

My next lens I am considering is the Canon EF-S 10-22mm f/3.5-4.5 USM Lens for my 500D. I will use it mostly on landscapes and inside buildings, etc.
This lens has some fantastic reviews, but is pricey, is there an alternative I should consider or hold off until I have enough funds.
Also, I altrady have the Sigma 17-70 mm f2.8-4 DC Macro OS HSM, is the Canon going to give me much more in the frame?

 

[odd jim]

The canon 10-22 will be massively wider than your 17mm. I have one and love it to bits.

The best alternatives are the sigma 10-20mm and the Tokina 11-17mm. Both are less expensive but not as highly rated.