Thank you all for your input, all the info and experience I can draw from is very much appreciated.
Arthur, the issue with filters is not a deal breaker for me, I'm more concerned with the quality of the lens and want to get a lens I will be happy with (and if it happens to be a less expensive one, all the better) but I will definitely be using it for low light situations and night shots, for this reason I have ruled out the f4 lenses even though they are really great lenses and there are more to choose from. Also, it would be the II series I would get, thank you.
Andrew, thank you for sharing your experience of the Tokina. Hearing first hand always adds weight to reviews I have read that say pretty much the same thing. Thanks also for the suggestion of waiting for the new Canon - I had a quick google and I think it might be priced a bit high for me, however that search also turned up information on one that Tamron are working on as well, although that will be a 15-30 rather than an 11-24. Maybe I'll get lucky and win x-lotto while I'm waiting
Analog, I also appreciate hearing what you thought of the Canon. I have read there can be a bit of softness in the centre, did you ever find this an issue?