A little more than a year ago Bill English wrote a post about 3th party MOSS tools that I just came across.
It's an old post, but still a nice read if you are interested in adding functionality to your MOSS deployment in one of the following categories:

1. Collaboration
2. Security, User Account Management and Permissions Management
3. Search and Relevance
4. Workflows
5. Document Administration
6. Upgrade and Moving Content

The post can be found here: http://admincompanion.mindsharp.com/BillBlog/Lists/Posts/Post.aspx?ID=75