[leet]

if you want wide on a 40D get the 10-22
midrange get the 17-55 2.8 IS (or tamron 17-50 2.8)
telephoto get one of the 70-200s or 100-400

the only reason the 10-22 and 17-55 aren't L lenses is because they are EF-S mount, the optics are L quality though