Easy question, obvious choice. Let me just move on to the pictures (all found via tumblr or google, unless stated otherwise). I'm not good enough with words to justify and explain to you the perfection that is Brad Colbert/Nate Fick.
Ok, so obviously I couldn't decide on just one. Initially I got a list of about 30 different tropes (chosen from here), but I narrowed it down to a Top 3. As I am not really great at explaining things, especially when feelings are involved, I'm going to give you short summaries and some fic examples.