The 16-35mm f2.8 zeiss. It's not a special use lens for me- I see in wide angle first and then compress things when necessary. I do landscape, portraits, photo journalism all with it and the lower depth of field from the larger aperture makes some great effects.
Previously my favorite was the Canon 35mm f2.8 T/S lens. It opened up a new world for me for 35mm that I had been missing since 4x5 film just became too cost prohibitive to develop. (though still 4x5 slides stitched together make amazing "stained glass" windows)
I don't do weddings anymore, I'm retired from that bit o' photography- it was too stressful especially in the days of film and now I just don't need the money. Back then though I loved, and most often used, my Contax 28-85mm (which I used on a Canon f-1, nikon f-4 and recently had modified to use on Sony/minolta bodies) and for some nice selective focus still shots my 50mm f1.2 L was hard to beat. I used a 80-200 L sparingly during weddings.