Put up open house signs at the home and directional signs along the way.
If you subscribe to "Enhanced Listings" features at Realtor.com®, there's a place for open house information.
For those with a web site and/or web log (blog), place the information there a few days before.
Community calendar web sites are becomming popular. If they allow open house postings, place one.
Place an ad in the subdivision newsletter.

