Check this MSDN site/article out. Summarizes alot of information about customizing your pages and sites :)

These topics are covered:
How to: Customize Navigation
How to: Create a Minimal Master Page
How to: Customize Page Editing Toolbar Components
How to: Add a Button to the HTML Editor Field Control
How to: Customize the HTML Editor Field Control
How to: Customize the Asset Picker
How to: Customize Styles
How to: Customize the Content Query Web Part by using Custom Properties
How to: Display Custom Fields in a Content Query Web Part
How to: Create a Custom Field Control (Movie Control)

Link: http://msdn2.microsoft.com/en-us/library/ms563713.aspx