Developing an application server: django vs. zend vs. cakephp vs. codeigniter vs. other
All of the frameworks that you mentioned are capable. Pick one in the language that you know the best and use that.
I'm trying to develop an application server that will deliver content to a core group of websites, as well as provide third party services to other websites that also want to use this content.  The app server will be hosting web services for these core + 3rd party websites.  Authentication and all that comes into play.  The data itself will consist of millions of records.
These records will come from a variety of sources: APIs, RSS feeds, REST services, etc.  This app server will essentially collect this data on a routine basis, and update the database with this new information.  This data will then be shared via some sort of web service (most likely REST) to the core websites and 3rd party websites.
FYI, I'm making a distinction between core sites and 3rd party websites because there will be different access levels, i.e. a core website will have more access than a 3rd party website.
All that said, I'm trying to make the best decision on which framework to use.  At the risk of losing all credibility, I currently have a ton of this code written as a wordpress plugin.  What started as a one-time site evolved into several sites, and some homebrew hacking to make my outdated infrastructure work across multiple sites.
I'm looking to migrate all of this to a new application server, with a solid framework.
Since everything is written in PHP, obviously I'm tempted to do the migration in PHP.  However, I'm considering Python because of its powerful ability to manipulate data.  I don't know if it's worth the hassle, though, of rewriting a lot of code in Python.
Could anyone give me some tips on what I should do?  I'm really looking to clean up a big mess more than anything, and would like a framework to encourage some solid programming conventions.