Church Multiplication Associates - Great site for information and resources produced by thoughtful doers.

The Well - A network of simple house churches that used to be a small, conventional Baptist church.

House2House - Details on conferences, a magazine, articles, a bulletin board and a store devoted to the simple church movement.

Dawn Ministries - Devoted to mobilizing the body of Christ for church planting.

Simple Church Video - An excellent primer on the simple church movement by some experienced and thoughtful pioneers.

When You Come Together - Another free video with some helpful ideas.

Home Church Help / New Testament Church Life - Contains a ton of useful information and ideas compiled by a guy who's doing it.

Subversive1 - A website loaded with insightful writing on relevant topics and a really good blog, hosted by a delightful simple church leader/practitioner.