Let's start...

Damon&Elena - Grenade/Bruno Mars
( Damon's side)

Katherine: Beautiful Monster

-> Damon&Elena - Hold it against me/Britney Spears
(Damon's side) lyrics are pefect,but it would be better,if the song is slow.

Damon: Tonight I'm loving you/Enrique Iglesias
About how Damon use all this women,just for playing.

Damon&Elena: Just a dream/Nelly
(Damon's side)

Elena: Only Girl/Rihanna
Because both of the Salvatores loves her and she feels like the only one.

Damon&Elena:We cold make love/Jason Derulo