This article is several years old now, and much has happened in Umbraco land since then, so please keep that in mind while reading it.
Here is a short screencast on one of my favourite packages for Umbraco, DocTypeMixins. It's just one great example of the packages created by members of the Umbraco community that make using Umbraco such a joy. Apologies to anyone who saw me give this presentation at the last Glasgow Umbraco Users Group (GLUUG)!
The package was written by Pete Duncanson and Matt Brailsford, and you can get it here on our.umbraco.org.
David is on Twitter as @dconlisk