The one that always sends me into fits of laughter:
Sheldon: "Priya, if you're experiencing any tension or awkwardness, it may stem from the fact that Leonard and Penny used to, if I might quote Howard, 'Do the dance with no pants.'"
Last night's episode.
Drunk Sheldon, outside his own bedroom: *knock knock knock* "Empty room?" *knock knock knock* "Empty room?" *knock knock knock* "Empty room?" (To Amy) "I would have freaked out if someone answered."