Mike Cohn has completed his latest book on Estimating and Planning. I've been able to read the previous drafts and have been very impressed.
If your only experience has been with predictive project management techniques where your estimate from day one of a project is held over your head at the end of the project, you will be inspired by the ideas in Mike's book.
Read the sample chapters on Mike's website, then buy the book when it comes out on October 21, 2005.
http://www.mountaingoatsoftware.com/agileplanning
Mike Cohn also sent along a blog entry about a Planning Poker. If you've never played, I suggest it highly!
http://blogs.msdn.com/dave_froslie/archive/2005/09/30/475791.aspx