What about a 24-70? If you can afford it, the F2.8 version is supposed to be top notch. I have the F4 and find it to be an excellent performing lens. While I'm sure the extra speed of the F2.8 would be a plus in many situations, I'm sure you could deal with the extra stop of light required with the slower lens. Both are S line lenses. The 28mm F2.8 is not.
I would think a normal zoom would be very handy in shooting weddings. FYI, I've only shot one and that was a case of me doing it for a friend, or folks with Instamatics being the only record. Yes, that was a long time ago. Anyway, if things are tight, the 24-70 would give you that bit extra at it's widest over a 28mm, but would also allow you to zoom in to 28 or 35, or whatever you needed without moving the camera position.
If you already have one of the two, I would think you would be covered.