I have use APS-C bodies for events and my setup goes like this -

Sigma 10-20mm f/4-5.6 HSM
Nikon 18-70mm f/3.5-4.5 AF-S
Nikon 80-200mm f/2.8 AF-S

My main lenses were the 10-20 and 80-200. Most of the time I move myself to compensate the mid-range. If I interfered other shooter or videographer, I change my 10-20 to 18-70mm.

As what many said above, there isn't any best lens combo but there is such thing as best lens to do get your assignment done happily.

For your Canon counter part, get the 17-85mm since in wedding receptions, you will blast your flash more than anything else so do not worry on aperture for now.

For the tele-zoom, I would suggest a 70-200mm f/4 first. To start with. Alternatively, you can go for Sigma 70-200mm f/2.8 or if you are crazy enough, get the legendary 80-200mm f/2.8 L USM. The reason I suggested the f/4 is to safeguard yourself in investment and also a stepping stone to your passion.

Invest yourself 2 sets of speedlite. This is very very essential when it comes to indoor shoot. Get yourself a set of good rechargeable batteries and trust me, no lens can shoot pretty without proper lighting.

I didnt realize the existence of 15-85mm till I see its release news with 7D

I can vouch 17-40mm L is the best valued L lens you can get. I carry one when f/4 does the job in my assignment. That was the first Canon lens when I jump ship recently