We just bought our daughter the Canon 10-22 for her 2nd trip to
Germany (she shoots with a Digital Rebel XT).  So far she has the 50mm
2.5 macro & a cheap 75-300 and now the 10-22.  I don't want her to be
(nor do I want myself to be) a 'Canon snob', but I can't help sticking
to the  camera lenses (I have all Nikon lenses for my Nikon).  

We're looking to get her an intermediate zoom lens (in the 20-80 range
to 'fill the gap' as it were).  The obvious Canon choices are the
24-70/2.8 (~$1200) and the 24-85/3.5-4.5 (~$300).  I suppose the
17-40/f4 might fit the bill as well as might the 24-105/f4.  

Now, surely you get what you pay for, so the 24-70 should be far
superior to the 24-85.  She mostly takes landscape and macro shots (a
strange combo to be sure).  She has an offer to shoot someone's
wedding, though I already cautioned her about the pitfalls of wedding
photography.  If she can get the occasional wedding gig, she can
surely buy whatever lenses she wants.

So I guess my questions are:

Does anyone have experience with both the 24-70/f2.8 and the
24-85/f3.5-4.5?  Is there a serious performance gap?  Would either
work for a wedding, or would the inferior optics make for poor photos?

I read somewhere that the Tamron 28-75/f2.8 is a good lens; anyone
have that or any other 3rd party lenses for Canon that they like (in
this 20-80 range)?

Any input is greatly appreciated.

Bob