For the telephoto area, have you looked into the Sigma 100-300mm F4? This lens is really sharp, fast, and image quality is near prime lenses. One advantage for this lens to the Canon 100-400 is the constant aperture. You loose the IS, but if you are doing surfing images,the ISwon't help to much. If you then add on a good 1.4x TC (a good Sigma DG model) then you will have a constant F5.6 lens. If you really want more light, then the Sigma 120-300mm F2.8 is the bet. A few other options are the Sigma 50-500mm (Bigma), Canon 100-400mm IS, and any of the Sigma or Canon 70-200mm F2.8 lenses with a TC. For the Sigma lenses and TC's, look at the DG models. They have new coatings to work with digital cameras, and fight against CA.
For walkaround lens, any of the L or Sigma EX will give you great images. One of the advantages to the 20D and the 30D is that they are more sensitive with a F2.8 lens. They have more focus points in the center area. You do not see these, but they are used to be more accurate. Any of these will work, as the Canon 24-70 and 24-105 are great lenses. Also, the Sigma 24-70 and Tarmon 28-75 are right behind them on image quality.
For the wide end, both of the lenses that you mentioned are great. They both can produce sharp images. What you will have to watch for is the housing. Which will work in that.
Hope some of this helps