Sigma 10-20mm f/4-5.6 or....

[Nifkin]

If you don't fancy Simply Electronics, the Canon can be had from Onestop-Digital for £489 (advertised at £499, but you can get them to pricematch).

Yeah, and Kerso has a good price on it too, a wee bit more but you get a UK-valid warranty with him. I'm often tempted by Onestop, but, with lenses at least, you never know if you're going to get a good copy, and having to send it back to Hong Kong seems like a lot of hassle to me.