SharePoint is a great platform, and there are several additional features available for free. I have collected some of the good things from the community and elsewhere

Application templates and role-based templates
40 application templates for SharePoint sites and 7 role-based templates for SharePoint MySite. Go get it at http://www.microsoft.com/sharepoint/templates.mspx

CKS - Community Kit for SharePoint
At CodePlex (CodePlex is Microsoft's open source project hosting web site) there is a Community Kit for SharePoint (CKS) that have many valuable elements. "The Community Kit for SharePoint is a set of best practices, templates, Web Parts, tools, and source code that enables practically anyone to create a community web site based on SharePoint technology for practically any group of people with a common interest."

• Enhanced Blog Edition
• Enhanced Wiki Edition
• Corporate Intranet Edition + + + several other edition
• Tag cloud
• Taxonomy tagging
• Virtual Earth maps on SharePoint
• Solution Sharing Network (SSN)

Governance related tools
SharePoint governance and manageability in CodePlex (http://www.codeplex.com/governance)

Faceted search
Faceted search, or post filtered search, is a common request. MOSS 2007 doesn't have this feature out-of-the-box. There are several third party solutions for MOSS 2007 that target this request. In addition there is an option at CodePlex that might be good enough. The faceted search project available at http://www.codeplex.com/FacetedSearch/

Other CodePlex features
The list is long, and there are several good features not mentioned in this blog post. Enjoy the whole list at http://www.codeplex.com/Project/ProjectDirectory.aspx?TagName=Sharepoint