Below are a list of books and e-texts I’ve personally found helpful. Feel free to suggest more in the comments below.
The Project Gutenberg EBook of Kalevala: the Epic Poem of Finland — Complete, by Elias Lönnrot (This is the edition of the Kalevala I reference throughout the site because it’s freely available and not under copyright restrictions).
The Kalevala: An Epic Poem after Oral Tradition by Elias Lönnrot (Keith Bosley translation)
Magic Songs of the Finns – spells in English (Collection of prayers/spells translated in 1896 in a collector’s edition from the Pagan Archives).
You can also find very detailed and extensive bibliographies at the site below. I do not list all of the works on these lists, as I have not personally read them, but this is what I consult when poking about for something new to read.