Ohhhhhh this is fun!!
I appreciate a good many, but my number one fave is what the Japanese call tsundere. The "boy and girl meet, hate each other and refuse to budge about it....but involuntarily come to realize the other isn't as bad as they thought and realize they're each others perfect match and right for no one else" ala Pride and Prejudice, Beauty and the Beast, all that good stuff :)
My second fave is "boy and girl meet and like each other and fall harder than they thought, but due to many abounding circumstances can't bring themselves to say it aloud...at all" ala Once. It was actually Once that made me realize what plot devices move my soul.
And of course these two tropes usually work in conjunction with each other, but here and there they don't.