One of my favourite photographs of all time is Robert Doisneau's Kiss by the Hotel de Ville, taken in the 1950's.  It is the perfect candid street photograph capturing that decisive moment.

http://www.masters-of-photography.com/D/doisneau/doisneau_kiss_full.html

I am thinking of doing a kissing project myself this Christmas and take photographs of people kissing, some candid, some posed .  Hopefully it will engender lots of love and good will.  I'm not sure I'll be allowed to publish the results but I will see what we come up with.