Could it be Mer? Here's the scoop from TVGuide's Michael Ausiello.

Grey's scoop, please! I hear someone may be preggers — and that someone shared a red-hot smooch in the finale!
Now that the Grey's finale has aired, can you tell us which kiss was the "major" one that Shonda Rhimes was talking about? Based on her morning-after post-mortem, I think she was referring to Mer/Der's big smooch. Personally, the Alex/Izzie kiss was the only one that made me lean into the TV.
I just watched an interview with Patrick Dempsey where he mentions that the next season of Grey's Anatomy will be 30-34 episodes long. Any scoop on that? Really? He said that? My sources are telling me it'll be closer to 24 episodes.

Plus, here's Ausiello's grade on the finale.

B+ (Ellen Pompeo has never been better. Ditto Justin Chambers. Loved the final shot. Shonda Rhimes, consider thyself redeemed.)