The new Canon digital camera shipped today, so I should hopefully have it by Tuesday. Turns out a bunch of my co-workers shoot with SLR's which use Canon lens mounts, so I may try out a few of their lenses before I pull the trigger one a new one myself.
The leading contender right now is a 28-135mm IS USM lens from Canon. (Due to the 1.6 focal length multiplier in the 10D, this ends up being something more like a 45-216mm). Although a fixed, prime lens would be a lot cheaper, I see a lots of folks raving about the Image Stabilization feature helping them catch shots they'd otherwise miss in the field when they're without a tripod.