From where can i start magento extension development

[JackITo]

I am familiar with magento and also wrote some widget for magento as well , now i want to create some magento extension, Can you please help me out from where can i start the magento extension programming . Please advice me good tutorial and books

[davidkroj]

I hope you can get some idea's with this link http://www.magentocommerce.com/magento-connect/create_your_extension/