personally I dislike the lead male and female becoming romantically partnered at a random time. If it's romance or they already are in love it's alright. However, this way is done to death so it's hardly surprising anymore and it undermines the meaning of the secondary chararacter's existence!
I could name many, many occasions of this but it's (now weak, it's overdone) spoilers.
The title explains itself fairly well. Nothing reffering to indecent films/episodes/specials (usual forum rules anyway), and they have to be reasonably common. Finally, they have to be existent in more than one franchise. Other than that it can be anything.