I've long known that Tolkien favoured dwarves to dwarfs as the plural of dwarf but, living post-Tolkien, it's easy to forget that dwarfs was ever the preferred spelling. Then it was pointed out that the Disney film (which came out the same year as The Hobbit) is Snow White and the Seven Dwarfs. I don't think I ever noticed that before.
It was pointed out by Aardy R. DeVarque's Sources of D&D page which is an interesting study of the origins of many terms in the original D&D (hint: they weren't all from Tolkien!)
UPDATE (2007-12-09): Mark Liberman talked about /-fs/ vs /-vz/ plurals back in 2004 in The Theology of Phonology with a followup specifically on Dwarves vs Dwarfs.
The original post was in the category: linguistic_observations but I'm still in the process of migrating categories over.
The original post had 7 comments I'm in the process of migrating over.