Codeigniter has been all but abandoned by EllisLab, the community is giving up on it and there are far better frameworks available now. For example Laravel, the growth that Laravel is experiencing right now is huge, it has overtaken Codeigniter as the most popular PHP framework on GitHub and has a growing and active community. Anyone even thinking about Codeigniter any more is doing themselves a disservice, Laravel is leaps and bounds ahead of Codeigniter. Laravel is on its way to being the Rails of PHP.
I recommend FuelPHP [1] - it has amazing documentation, a lot of built-in libraries, takes advantage of PHP5 features, is quite mature and really easy to dive in.
http://www.google.co.uk/trends/explore?hl=en-US&q=laravel,+s...