I am going to buy the canon 20d. My main interest is scenery, street scenes and children. I am not going to carry more than one lens. I dont mind to carry an extra 1 kg. I am aware fo the different cost. I consider Sharpness and true color very much.

Would you suggest the canon 24-70 l2.8 or the canon28-135 3.5-5.6iIS USM

the 24-70 hands down is going to blow the 28-135 out of the water.

If you're still checking in (and haven't made your decision), save yourself some money and have a good look at the Tamron 28-75mm f/2.8 Di. Comparable to the Canon L 24-70mm f/2.8 and about 1/3 the price!