Many thanks, Mike, Chris, Dave and Collin for your replies. Thanks for the offer Chris. I have just done a search and now leaning towards the Tokina 11-16mm f2.8, with reviews saying one of the sharpest in the range even compared to the Canon 10-22.
http://www.tokinalensreview.com/ Only down fall I came across is the CA that can be removed in processing.
Thanks Dave for your info on fisheye lenses, think I will stick to the rectilinear lenses.
Colin I will check the price on that lens as your results are impressive.
All the best.