No Gurren Lagann?
This must be rectified.
http://www.youtube.com/watch?v=GopzpFJm4LQ
Also:
http://www.youtube.com/watch?v=Iof5pRAIZmw
Or for less "GAR YEAH I CAN DO ANYTHING" kind of uplifting and more of the "So happy now I think I have diabetes" kind:
http://www.youtube.com/watch?v=eWM2joNb9NE
http://www.youtube.com/watch?v=NUrNf2V52LQ
My Little Pony songs are also good for the latter kind of happiness, but any brony will already be self-recommending those, and not many non-bronies are likely to be fond of them.
(But I'd suggest Giggle At The Ghostie and Pinkie's Singing Telegram in that case, because Pinkie Pie is awesome)