I've worked with codeigniter since 3 years back. I did lots of projects with it.
So I decided to build a course on codeigniter for beginners who is trying to learn it.
This is course if for beginner of codeigniter who has prior knowledge in PHP.
You can get it from here - http://www.udemy.com/codeigniter-learn-it-correct/
You've to pay a small fee for that but it worth your time since I always try to make it simple and to the point. So you can learn what you should learn in less time.
If you still looking to learn codeigniter. But not ready to pay yet :)
Don't worry I know that, take this introductory video on youtube - http://www.youtube.com/watch?v=qux5rgihIY0