Kings of War is a new set of fantasy rules from Mantic Games, who make some very cool figures. But the rules are non-figure-line specific. And they’re free.
A Spot of Friendly Wizardry is a set of free game rules for duels between two wizards.
From Impact Games, Elfball is a set of fantasy “football” rules. It’s played on an oval field, so it’s not like “American Rules.”
Plastic Attack is a simple set of free wargames rules for playing games with your plastic action figures.
Merlin Rouge is a fantasy supplement for the You Are Still My Lord Wars of the Roses rules. Both rules sets at the link.