Ensiferum - Iron
Don't call this album Viking metal. It's definitely not (although their later stuff is). It's just damn good melodic death metal. Iron, to me, is why I think of partying (as much as you can to metal) when I think of melodic death metal. It just sounds really happy, and it's really easy to sing along with. No complex music to follow, just good and simple fun.
Fave tracks: Sword Chant, Slayer Of Light, LAI LAI HEI