Try Could Well Be In by The Streets, and if you like that, try the album from that song, A Grand Don't Come For Free. His rap is satirical in nature and quite funny and witty, and it's -mostly- light-hearted. You could try Das Racist's Puerto Rican Cousins, which is also a fun kind of rap. Gone by Kanye West is also a really good song that's light-hearted and very easy on the ears.
Really though, light-hearted and rap rarely go together. ;
Spiritualized - I Think I'm In Love