Go for the IS. You really need it on telephoto lenses... and its easier to resell if you ever decide to sell it. In my local area there are three or four f/4 non IS versions on the market, but only one IS model.
I respectfully disagree. Whilst IS is great to have for long lenses, it's mostly being used for more stationary subjects (paparazzi/wildlife). The situation changes for action photography. Say you're shooting at 200 mm (cropped frame), you'd need a 1/300th shutter speed to prevent camera shake in your pictures. IS would allow you to use ~1/30. Now I dare you to shoot sports at 1/30th. The only sport pics that would turn out well are chess pics
No, you need fast shutter speeds for sports. IS is nice to have, but a large aperture beats it. Check out my review on the sigma 70-200 f/2.8 in the user reviews section if you'd like to spend a bit less, or buy the canon 70-200 IS f/2.8 if you're richer than me and value the addition of IS for non-sports photography.