The episode featured a number of almost-kisses, but you can see the real thing toward the end of the clip:
The whole thing is pretty chaste, and it's not center-stage, perhaps because of Mitchell's shyness about public affection. Modern Family executive producer Steve Levitan implied in August that Mitchell's coming to terms with said shyness had always been a planned storyline, saying the creators had always meant to feature a kiss "as part of the natural development of the show." He also said that viewer discontent with Mitchell's standoffishness was "unfortunate" — but it's not hard to see their point of view. Though TV has featured a number of dude-on-dude kisses over the years (the first primetime one may have been on Dawson's Creek!), they're still not as common as straight smooches, and it would be nice to see physical affection between gay men treated as both sexy and normal. Now that they've kissed in public, hopefully we'll see Mitchell and Cameron get physical more often. Meanwhile, Oprah has some more advice for Modern Family: make some black friends.
Given that TV in general and gay characters in particular are still overwhelmingly white, it's a good call.