CodePlex has some cool projects for SharePoint. There a few well known projects like the WSP Builder, Community Kit for SharePoint, SmartPart and STSDEV that have been used extensively by the fraternity but there are also a lot more that make lives of the MOSS guys easier.
One of them is the SharePoint 2007 Features project has a nice collection of features that can enhance your MOSS environment. The features here help make little improvements that people always want on MOSS. Especially the features like Log Viewer, Print List, Share Point Events Manager and Unique Column Policy help add a new dimension to MOSS quickly. Another project that can be pretty handy in intranet implementations is Active Directory Tools for SharePoint.