I blogged earlier on how to enable MOSS with .Net 3.5 and had a link to a project on CodePlex that is no longer valid.  Once again, thanks to Kirk Evans for letting me know that the project has been rolled up into a single Codeplex project that has many different features for MOSS 2007.  Here are some of the highlights: 

Most Popular Features

Debugger Feature
Log Viewer
Print List
Toolbar Manager
Unique Column Policy (updated 3/3/2008)
Window Links

Developer-Oriented Features

Ajax.Config Feature
Content Type Hierarchy
Debug Config Feature
Global Web.config Feature
Minimal Master
Minimal Publishing Site
Placeholder Master
Silverlight (.NET 3.5) Config Feature
Regular Expression Validation Field (Added 6/11/2008)
Reset Theme (Updated 9/2/2008)
Theme Changer and ThemeChangerStaple
Variation Labels Field (Update 9/22/2008)

Administrator-Oriented Features (and supporting features for developers)

Clean Web Part Errors (Added 9/2/2008)
Manage Configuration Modifications Feature
Manage Form Users
Manage Hierarchical Object Store
Manage Application Configuration Feature (Added 12/9/2008)

Manage Layouts Site Map Feature
SharePoint Events Manager (Added 7/15/2008)
Site Creation in Target Database (Added 12/9/2008)

End User-Oriented Features

Anonymous Audience (Added 9/22/2008)
Presence Contact List
Task Alert
Task Mover (updated 3/11/2008)
Toolbar Manager

Unique Column Policy (updated 3/3/2008)