Depends on whether you want something for wide-angle landscape and architectural photography. The 24-105 is a great lens but is aimed primarily at full-frame cameras like the 5D and 1D series. On a 1.6x crop camera 24mm gives an equivalent field of field of 38mm, which isn't terribly wide angle. It would be OK if you also had an ultra-wide such as the Canon 10-22 or Sigma 10-20, but on its own you may find it limiting.
I'd also consider the Canon 17-40 f/4L which is an excellent lens for not too much money.