If you can spring for the EF 24-105 f/4 L IS USM that'd be my suggestion, though I don't have any experience with it outside reviews (which indicate excellence). For great info on Canon zoom (and other) lenses I'd suggest starting your reading here:
http://www.the-digital-picture.com/Reviews/Canon-Zoom-Lens-Reviews.aspx
Post 40D release, I'm finally ready to buy into the Canon lineup. Here's my plan:
Wide ... EF-S 10-22m f/3.5-4.5 USM
Mid ... EF 24-105mm f/4 L IS USM
Long ... can't afford a lady in white yet
Fast ... EF 50mm f/1.8 II