Outdoor midday and white dress.. tips?

I posted this in the wedding section, but it's probably better suited here as it's not really wedding related as much as it's about a tip for a specific type of shot. The venue just happens to be a wedding.

shooting a wedding in a couple weeks. I am worried about blowing out the whites in the dress. Any tips to avoid this?

I will be using the 50mm 1.8, 28-135, and 70-200L along with a 430ex.

Should I be shooting with a filter and if so, can anyone recommend what would be a good choice should I happen to encounter bright sunlight and I don't get lucky and have an overcast day.

You've picked a most difficult shooting situations. First of all, I wouldn't shoot in direct sunlight as you're almost guaranteed to blow out the highlights on the dress to get a good exposure of the face. Move the subject into open shade and shoot there. Use RAW to get the most from the shots (and to be able to adjust white balance in post processing).

There's not really any filters I can think of to help in the situation - it's a matter of contrast and dynamic range rather than of anything else. You could try reducing the dynamic range and contrast by using a white reflector to throw some light onto the subject's face, but this will be of only limited help.

Here's a shot where I coped with the problem by putting the bride and groom in open shade.

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Yep, this is a difficult situation. Shooting white clothing outdoors in midday sun will almost certainly lead to blown highlights in the dress unless you really work to prevent this. My best tips are the same as those already mentioned, move them into open shade if possible and definately shoot in RAW, also I would unabashedly chimp the first couple of shots to make sure you've not still blown out all the detail on the dress.