CNN is carrying a mental_floss article about the Ten important kisses in history. As could have been expected, the kiss that Judah gave Jesus is in the top spot:
Nothing ends a good “bromance” quite like flagrant, murderous betrayal. A long time ago, a wandering preacher named Jesus was doing pretty well for himself — building up a following and promoting religious teachings — until one of his buddies sold him out to the authorities. In exchange for 30 pieces of silver, Judas Iscariot kissed Jesus on the cheek and, by doing so, identified him to Roman soldiers.
Although Judas double-crossed his best friend for a paltry sum, some scholars argue that Judas is the secret hero of Christianity.