KOOL's "Sarishinohara" comes to mind immediately. He happens to sing ballads with a lot of emotion.. His voice gives off a calming effect whenever he sings ballads too.
I try to avoid ballads and sad songs cause I'd be sitting there for maybe 5 - 10mins afterwards sobbing and trying to explain why I'm crying.
As for the funny side.. I've probably cried a few tears laughing at the silliness of Kouhey's cover of "Rolling Girl", not his hard rock cover, the original one which he mashed-up with a somewhat NSFW song.
EDIT: Pokota's band cover of "Eh? Ah, Sou" gets a mention, mainly cause of the guitarist, KIKKUN, dancing around.