I'm not a Canon person, but I just read a review on this lens in one of my photo magazines. That's the one I'd be saving for.I have two favorites.
The canon 70-200 f2.8 L Is; it is an excellent lens, but very pricey
I keep the canon 17-55 f2.8 IS on my camera most of the time and I love it. This lens is also a little pricey.
Before I bought the 17-55, I used the 50mm f1.8. It is inexpensive and has good image quality. Also a good focal length for portraits.