Which circular polarising filter for 10-22?

I want to improve the skies in my landscapes taken with my Canon EOS 350D and Canon EF-S 10-22mm lens. Do I need to spend £130 - 160 for the thin Canon or Hoya circular polarising filters or would a standard (thicker and much cheaper) 77mm filter do? Anyone got any experience of this combo? I am worried about vignetting but I should say that I rarely use the lens at the widest end of its range.

With the 10-22 you should get a thin filter. You're looking at up to 96 deg. of coverage and vignetting will be an issue with too thick a filter.

But be aware that a circular polarizing filter with an ultra-wide lens won't be able to uniformly darken the sky. The extent that polarization affects the sky varies with the angle to the sun's rays, being strongest at right angles to the sun. With the wide angle of a 10 mm lens, you'll notice significant differences in the sky colour from edge to edge. You may be better off using a graduated neutral density filter to let you hold back the sky exposure while giving the foreground a bit more light. See also this thread.

Thank you for your comments and the pointer to the ND thread. I used to use both polarising and graduated ND filters (Cokin) with my Olympus OM 2N film camera many years ago. For our current wintery skies I thought a polariser would be what I need first and I intend to save up for some ND stuff for the summer. Sounds like I will need to pay up the extra for a thin filter. Which one though - Hoya Pro or Canon?

Yes, the 10-22 definitly needs a slim filter.

The Hoya Pro1 with front threads starts to vignette at 12mm, so any cpl with no front threads should do it.

Now the Hoya ones are a bugger to clean... I have no experience of the canon, but have heard many members hear say god things about B&W CPL filters...

Really? I have the Kenko Pro1 Circular polarizer, which is supposedly identical to the Hoya Pro1 and they do not vignette at 10mm. I've heard reports from others as well that the Hoya Pro1 does not vignette. You will prefer the front threads for your lens cap over the dinky rubber caps you have to use with the filters with no front threads.