How to create new wordpress widgets for my themes ?

How to create new wordpress widgets for my themes ?

This is my favourite tutorial about that:
http://justintadlock.com/archives/2009/05/26/the-complete-guide-to-creating-widgets-in-wordpress-28
I'm using it as a base to all my widgets.
Basically, the widget is a plugin, but you extend the class WP_Widget. It's quite easy, just follow that tutorial.
Also this is helpful http://codex.wordpress.org/Widgets_API
Good luck!
This is more a question for google than stackoverflow. You'll find tons of tutorials and examples on the web.