WordPress is available from the project's home page, www.wordpress.org [1]. However, you can download the latest code in .tar.gz format from wordpress.org/latest [2]. I found this to be an especially clever and useful way to ensure that a single URL always has the latest version. The WordPress site includes documentation, active support forums and a Weblog describing the latest development efforts.
Links:
[1] http://www.wordpress.org
[2] http://wordpress.org/latest