I went through a huge viking metal phase about twelve years ago. I usually keep all my viking metal CDs in the same section as the Folk Metal, and Pagan Metal. I tend not to make too close a distinction between these three so called genres.
My favourite viking metal bands are: Thyrfing, Einherjer, old Enslaved, Falkenbach, and the first two Tyr albums and Moonsorrow. I do include Moonsorrow as a viking metal band as their first few albums in particular were very much on those themes.
Just amazing stuff. I was pretty obsessed back in 2001-2007, walking around listening to these bands and thinking I was olde school Odin. Good times.