Everyone I've been talking to in different stores have said IS is the "must-have" on any of the lenses. But they probably have a economic incentive to make me shell out more for an IS lens ;-)
For the longer focal lengths, IS is indeed a big help when using a lens hand held. To use a non IS lens you need to crank up your shutter speed. For moving subjects, a high shutter speed is required in any event, but for many of your shots, light may be limited, and if the subject is still or moving slowly, IS is a huge help.
Since you have the 24-105mm IS, the 100-400mm IS complements it perfectly. The three lenses you listed are all excellent, the 70-200mmL's are a little better, but all are excellent.