There is a similar topic for Black Metal, and I really love the formula, because it gives an opportunity to analyze deeply the subgenre. Best band or best song is ok, but it's kinda unfair for bands who are not very famous but have strong points. Just give a top 3 for these three categories and give short explanations if you want, but don't exaggerate, unless you want this topic to be overloaded with useless information...

1. Top three Folk Metal bands

2. Top three Folk Metal albums

3. Top three Folk Metal songs

My personnal top 3's are the following:

Best Bands
1- Equilibrium: To me, no band in the world masters better the epic feeling of Viking Metal.
2- Korpiklaani: One of the rare bands who are Folk with metal elements and not the inverse.
3- Orphaned Land: The Middle-Eastern melodies are just delightful.

Best albums
1- Sagas (Equilibrium): Certainly the album I listened the most to in my life.
2- The Varangian Way (Turisas): Too short, but the symphonies and vocals are masterful.
3- Mabool (Orphaned Land): About the only prog album I love from the beginning to the end.

Best Songs
1- Unbesiegt (Equilibrium): So epic, so beautiful, so fast, so brutal, so WOW!
2- To Holmgard And Beyond (Turisas): I'm ready to jump on a drakkar and conquer the world, my Lord!
3- Ocean Land (Orphaned Land): You could dance balladi on that METAL song. Isn't it weird? No, it's beautiful.