Nathan Fillion
"Castle Walls" - T.I. w. Christina Aguilera
http://www.youtube.com/watch?v=Z0dF6TvkcvU
(he's the star of Castle)

Taran Killam
"Here It Goes Again" - OK Go
http://www.youtube.com/watch?v=dTAAsCNK7RA&ob=av2n

(though it is hard to beat Call Your Girlfriend as a pick, this the the more obscure choice-- he had a web series called Nobody's Watching like 5 years ago that got turned into an never-picked-up WB sit com. The OK Go pick comes from this short video: http://www.youtube.com/watch?v=x49WZRyXGe0)

Retta
'Pony" - Ginuwine
http://www.youtube.com/watch?v=_tMluz0R1LU

(her character on Parks & Rec is supposed to be his cousin)