My OTP is Chair (Chuck & Blair), and I have two favorite scenes of them. The first one is from season 2, episode 13. Chuck's dad just died, and he came to Blair for comfort. Here's a link to watch the first scene:
link
The second scene is from season 3, episode 12. It's the one year anniversary of Chuck's father's death, and Chuck thinks that his dad would be disappointed with the man he's become. Serena gets into an accident and is sent to the hospital, which causes Chuck to relive the night of his father's death all over again. Of course, Blair is there to comfort him. Please watch the videos! The second scene is the one posted with this comment.