Bayou Seco do the New Mexico Wedding Polka. (very traditional there) A really good mixer. (Google for them - they are over here soon).

Basically it is an interrupted tune, you play a slow dreamy pace, shout dance, then a fast pace

Two lines (men and women) facing one to one. The odd one out has a broom - actually besom stylie - and that person mooches in time to the music up and down the avenue (points for artistic expression) until the slow music stops - every one grabs a partner and any oddbod has to pick up the broom (to polka with). then the music speeds up and every one polkaing until the music stops (or reverts to slow with a shout "lines") and the lines re-form with the new oddbod mooching.
repeat until done! Couldn't be much simpler.

Horses Branle is another good mixer and gender unspecific and simple. Dashing White Sargent accommodates gender inequalities and is a bit more complex.

If the Bride & Groom are a bit experienced a waltz like Rosa might work. Otherwise you may have to play a ballroom type waltz for the hitched pair to start the dancing.