Another vote for the 10-22, and sell it if/when you upgrade. Don't forget, that upgrade might never happen, but if it does the 10-22 will keep its value.
Also consider the Tokina 11-16 and Sigma 8-16 as faster/wider alternatives respectively, but they probably won't hold up their value as much as the Canon lens will (or buy them 2nd-hand now).
Or even look at the Sigma 12-24 mk1 or mk2 (mk1 for minimal barrel distortion, mk2 for [centre] sharpness), that you can keep if/when you go Full Frame.
(Or if you really have the cash, and don't mind post-processing work, a ts-e 17mm can take nice parallax-free panoramae to stitch together later, not sure how 'wide' an equivalent lens it makes though)
But yeah, either way, the 17-40 is not really ultrawide on a crop-body, and not the sharpest either, a dedicated wide to ultra-wide is the way to go for now.