I took this from
LOTR
I.Dom/Elijah
2.Orlando/Elijah
3.Viggo/Elijah
4.Viggo/Orlando
5.Aragorn/Legolas
6.SeanBean/Elijah
7.SeanB/Dom
8.Karl/Elijah
9.SeanB/Orlando
Harry Potter
10.Harry/Draco
11.Harry/Ron
12.Blaise/Draco
13.Fred/George/Draco
Vampire Chronicles
14.Lestate/Louis
The Dark Night
15.Batman/Joker
I don't see any similarities except I have a thing for blonds with brunettes and I also enjoy pairing someone masculine with someone delicate and pretty but that's not always the case with every pairing.
I also have a thing for bad boys they set me on fire still LOL!
Edit:You're also not opposed to turning canon animosity into sexual tension: Harry/ Draco, Batman/ Joker, Lestat/ Louis. That is such a turn on for me :)