That really depends on what you like to shoot. The most obvious issue with crop sensor cameras is, well, the "crop" that reduces the field of view in relation to a full frame camera. So you'll want to take that into consideration when choosing lenses, especially prime lenses.
There are two Canon zooms made for the crop format that are quite good: the 10-22/3.5-4.5 and the 17-55/2.8. Neither of them is built to the same level of quality of the "L" lenses for full frame cameras, but they make nice images. I own both, and use them with 40D bodies.
For a longer zoom, the 70-200 f/4 L IS lens is very good, and much lighter and less expensive than the f/2.8 version. I have the f/2.8 version, and want to buy the f/4. (The IS feature is very useful for me.)
For primes, the 50/1.4 and the 85/1.8 are nice short telephotos for portraiture, etc., with equivalent FOV of 80mm and 135mm respectively. The 135/2 has the field of view of a 200mm lens on full frame, so it's a nice fast medium tele (and very sharp.)
Not too many wide prime choices. The 24/1.4 becomes a 40mm equivalent, which is a nice focal length for street shooting, but it's a huge heavy beast. My copy of the 20/2.8 is pretty bad, though in fairness it's probably 15 years old.
If I had to do it over again on lenses, I would buy the 10-22 (which I like), the 24-105/4 IS zoom, and the 70-200/4 IS zoom, and probably a 50/1.4 and a 135/2. That would give me coverage from very wide to tele (~16mm FOV to ~300mm FOV), with two useful fast primes.
(Note that I would not buy the 17-55/2.8 again. It just has too much overlap with the 10-22, and it's not quite long enough on the long end for me. The 24-105 would solve both those issues. The 17-55 is a nice lens, though, so don't take this as a bad review. It just doesn't fit my shooting style.)
Also note that all of those lenses except the 10-22 will work on full frame Canon bodies, as well as the APS-H photojournalists cameras. So there is some room for future changes in your kit.
