i was in the same boat a while ago and my choice in the end was http://www.symfony-project.org/
* simple templating and helpers
* cache management
* smart URLs
* scaffolding
* multilingualism and I18N support
* object model and MVC separation
* Ajax support
* enterprise ready
i have used code igniter for many projects in the past but it really has limitations. Symfony is a entire development platform, debugging, etc. I could never go back to anything but Symfony now