The 17~40 will blow your budget and not really give you a good wide angle view. I have a 17~35 for my 10d and I have to change over to my old Coolpix or an Olympus E-20 with their wide adaptors for really wide shots. If you want to go that route, an I agree that wide sounds good for his needs, why not the 10~22 which will give him a really useful range for landscape and interiors?
I guess you're learning that there are no simple answers to this one...
