One of my collegeas, Bastiaan, pointed out to me a post regarding add-ons and tools for SharePoint which are now provided as open source. I'm not the greatest fan of open source but it has its advantages knowing how things are developed and their can be learned a lot from it. Some add-ons and tools which are now open source are:
http://blogs.msdn.com/sharepoint/archive/2008/03/24/several-very-useful-open-source-add-ons-and-tools-for-sharepoint-recently-released.aspx