WordPress.com:

• Starts off as free
• Is completely hosted by WordPress.com for you
• Extremely limited customization and monetization
• Does not include valuable access to WordPress plugins
• Is branded with WordPress.com’s logo and name in your URL
• WordPress reserves the right to delete your blog

WordPress.org:

• Requires web hosting and a domain to start with
• Has full access to thousands of WordPress plugins.
• Zero options are limited
• Full customization settings
• No limitations on how you monetize
• Your content is 100% yours