As above, there is Sigma and Tamron lenses as an alternative.
As has been recommended the Canon 70-200 F4 is a belter of a lens and well worth considering. The F4 version is much cheaper than the 2.8IS, the F4 IS version is approx 1/2 the price of the 2.8IS...
I went through a similar thing a year ago, I looked at - did I need the 2.8 over the 4 and also was the IS important or not (due to the extra cost). Do you want to buy new or are you happy with 2nd hand - there are a couple in the classifieds here.
I would say if you do want the Canon 70-200 F2.8 IS version then save up and get it, you won't be disappointed, don't plump for something else so you can have it now, as you'll probably look back and if only...