Here are the reviews on the Sigma lens:
http://www.fredmiranda.com/reviews/s...&cat=37&page=1
And those from a Canon 70-200 non-IS lens
http://www.fredmiranda.com/reviews/s...&cat=27&page=1
And finally Canon 70-200 IS lens
http://www.fredmiranda.com/reviews/s...&cat=27&page=1
Buy whatever you like ... its your money ... but the Sigma doesnt do to badly compared with the Canon lens though and is about $200-300 cheaper than the non-IS version