Heroes Among Us is a pay-what-you-want game for quick play superhero skirmishes.
Mike Fischer offers a set of miniature rules called To A Pulp (nice pun). He writes
Pulp gaming, in which each player controls a character or faction from a 1930’s pulp thriller, is growing in popularity. Such games combine the visual appeal of miniatures gaming with aspects of role-playing games, allowing the players to control the actions of tough private eyes, seemingly-helpless dames, brave explorers, and all the rest. I wrote these rules mostly for my own amusement.
The rules are made for simplicity and fast play. The game is meant for use with miniatures, but you can download a set of paper minis for free (see Section XI). All you have to provide is a few six-sided (d6) and ten-sided (d10) dice. The game is meant for two or more players, but it can be used for solo gaming as well.
Rattrap Productions has a set of free downloadable demo rules for its .45 Adventure miniatures rules. There also are a number of free scenarios.
Fallout is a legendary computer role playing game. Set in a post nuclear world, it has a 1950s science fiction aura. Here’s a miniatures game set in that world.
The Hot Lead and Steel Sinews Yahoo group focuses on pulp-era gaming. There are also a set of playtest rules for the period, called “Noir.” Unlike other adventure-miniatures games, this set of free wargames rules is specifically focuses on the period, featuring such things as “hero points” to capture the flavor of the pulp novels.