I'm an old movie buff, so for me- hands down- it's the kiss between George and Mary in It's a Wonderful Life.
They are squeezed together in this tight shot sharing the phone, trying to hold a conversation with a third party and trying to avoid what just has to happen. I love the desperate look in Mary's eyes, the hint of tears. And the way George, though trying to stay distant, keeps putting his face in her hair. When they finally drop the phone and share that series of really tender, yet really passionate kisses it is such a hard earned, great moment.
More modern and a bit more embarrassing, as I am too old to have watched this. The first time Pacey kisses Joey on Dawson's Creek. Mostly because I love watching him screw up his courage and then his agonized "Don't you ever get tired of just talking?" before he grabs her and lays it on her.
