Canon addressed this recently (in their full-frame sensor whitepaper, I think). In-camera Image Stabilization requires physical movement of the sensor. For short (wide) focal lengths, a little movment does the trick. But that's not where IS is needed. For long focal lengths, the sensor may need to move several millimeters, which isn't practical. So their view is that in-camera IS will never be as effective as IS that's built into the telephoto lenses.Originally posted by: fuzzybabybunny
DurocShark also had a good point with Pentax and Sony's DSLRs having built-in IS, so every lens has IS. Sigma, Tamron, and Tokina make mounts for these also, so the lens lineups are still extensive.
The choice is up to you. There are a lot of good options out there. I personally don't think Canon will come out with a body with built-in IS anytime soon, as this would cut into their own market for Canon IS lenses.