1. Castle & Beckett, 'Castle'

When the momentous smooch occurred: Season 3, Episode 13

These two lovebirds sure loved to hate each other. Of course, nothing was ever easy between Castle and Becket, including their first kiss. While working a case, Castle planted a big old smooch on Becket as a diversion from an on-coming guard. Although the make out session successfully fooled the guard, Castle and Becket couldn't fool themselves or the audience about their true feelings for one another.