Chris,
I recently shot a wedding as a second. I primarily used my 24-70mm f/2.8.
Personally, I'd opt for the 50mm f/1.8, 24-70mm f/2.8 and 70-200mm f/2.8 on the second body, as Stewart recommended.
I would suggest that you visit the venue as soon as you can and see all your vantage points so that you have some idea about the gear you'll need, but remember that your light will be hugely different on the day.
The next point is the style of photography - what you see as beautiful, the bride may see as horrid. Ask her to cut out some wedding photographs from magazines and give them to you. I'm sure you will see a pattern in the style she likes.
Decide on your timings, are you going to offer a pre-wedding shoot, bride getting ready, boys in the pub....that sort of thing.
I know it's a long way off, but remember the little things - batteries, CF cards (or whatever yours takes) etc.
Look at as many wedding photography sites between now and August as possible - there are some fantastic photographers on here and there advice will far exceed my own......just try and stay on the right side of them, otherwise you will undoubtedly encounter the criticism previously mentioned. Think about asking a friend to be your second, or if they are more experienced, you being their second.
The biggest fear I had prior to the big day was that I wouldn't enjoy it - this was a day that I had been building up to for 10 years and for me to be faced with that possibility was mind-opener! As it was, I loved every minute of it, and I hope you will too. Now - get researching!!
