Led Zeppelin played by a string quartet? The mind boggles.
Well, let's see. Your prelate is subjected to more wedding music in a year than most people hear in a lifetime, thus is happy to hear you say that you wish to avoid the done-to-death stuff. I've heard everything from Wagner to Kenny G.
Wagner is better.
Most "Contemporary Christian" wedding music really is dreadful schlock. I'm often embarrassed for the couple when I see the looks on the faces of the congregation when it is played. Best to stick to the classics.
Here are some possibilities...
Bach: Arioso, Air on the G String, a movement from one of the Brandenburgs
Handel: Lots of stuff from the Water Music or the Royal Fireworks
Marcello: Psalm 19
Vivaldi: Excerpts from the Four Seasons, esp Spring and Autumn
There's much great processional/recessional stuff out there but relatively little of it is well suited to string quartet. However, your quartet members should be able to give you some guidance about what they know and have used before.
Good luck. Let us know what you choose.