Resource for SharePoint Site Definition

Deciding Between Custom Web Templates and Custom Site Definitions
http://msdn.microsoft.com/en-us/library/aa979683.aspx

How to: Create a Custom Site Definition and Configuration
http://msdn.microsoft.com/en-us/library/ms454677.aspx

Understanding Web*Temp.xml Files
http://msdn.microsoft.com/en-us/library/ms447717.aspx

Understanding Onet.xml Files
http://msdn.microsoft.com/en-us/library/ms474369.aspx

Customizing Site Navigation
http://msdn.microsoft.com/en-us/library/ms471078.aspx

How to: Create a Custom List Definition
http://msdn.microsoft.com/en-us/library/ms466023.aspx

Creating Content Types
http://msdn.microsoft.com/en-us/library/ms479905.aspx

How to: Add a Document Template, File Type, and Editing Application to a Site Definition
http://msdn.microsoft.com/en-us/library/aa978104.aspx