The iPhone-dev team recommends using the built in updater to get the latest version ... "Check for Updates" in your current version of PwnageTool. If you don't have luck with that, there are mirrors posted in the release announcement, along with notes regarding Installer.app/Cydia:
"Installer 4 Beta is included, it is added in any mode by default. The main installer package management interface within PwnageTool isn't enabled yet, and will report that installer.app isn't available, but the actual Installer.app package is added as a default option in both modes."
"The latest Cydia is also enabled by default."
Happy jailbreaking, and the usual disclaimers apply: back up your data, use at your own risk, and remember that Apple does not support software like PwnageTool.
Thanks to everyone who sent this in!