Planet 28 is a set of free wargames rules for “quick narrative games between warbands of warriors, mutants, and outcasts.”
rules
Warpath Rules
Mantic offers its Warpath science fiction rules free for the downloading.
Peep Wars Wargames Rules For Marshmallow Candies
What do you do with all of those leftover Easter candies like marshmallow peeps and jelly beans? Play a wargame, of course. Invisible City Productions has rules for just such a scenario, called Peep War
Rules By Ral
The Mainly 28s site has the original Rules By Ral fantasy rules sets.
Zeppelins Over London
The endlessly interesting Junior General site has a new game called Zeppelins Over London.