Where online can I post my (free) rules and materials for games I've created?
I'd say the first place that jumps to mind for me is boardgamegeek.com

This forum seems like an appropriate place to post your rules and materials:
http://boardgamegeek.com/forum/26/boardgamegeek/board-game-design

You might consider setting up a tumblr or some other website you control and link the materials and information in the forum.