Which port should I set my service to listen to?
The normal choice is http-alt(8080).
I want to create a website which will serve more like a web-application. There will be two parts: the front-end (probably in PHP, Apache) and the back-end services (in Python,  using Twisted)
The front-end will usually provide some JavaScript which would send Ajax requests to the Python services and receive data back.
Since Apache will be listening on port 80, the Python services should listen to another port.
So my question is the following: what port should the Python services listen to? I am asking because I am afraid it might get blocked by the proxies, firewalls etc. that not so rarely get in front of the client's way. 
What would be the most standard, problem-free way to do this?