Web application: Programming language/Framework

Hi all

This is a bit off topic but I don't know where else to ask (please tell
me if you know). I'm going to build a web application. The choice of the
underlying database wasn't difficult. After a few preliminary tests I'm
confident that PostgreSQL is absolutely up to the task. But I'm at a
loss regarding the "middleware". I know Apache quite well, so I wouldn't
mind continuing using it. But what language/application server/whatever
do you recommend? Java/J2EE/JBoss, Struts, Perl, Python/Zope, PHP 5,
XYZ...? There are a few prerequisits such a framework would have to meet:

* Reasonably scalable.
* Works well together with PostgreSQL. An abstraction layer which
separates the SQL stuff from the rest probably wouldn't be bad either.
* Security:
    * I don't like to worry to much about buffer overflows, SQL
    injections and the like when coding.
    * The framework shouldn't need a security update every few days.
    * Support for encryption at the web frontend side and possibly
    on the DB end (OpenSSL being my favorite).
* Well established: Nothing that vanishes after a few months just
because it was the latest craze. Something where you find documentation,
mailing lists and a community.
* Free (open source) and free (or reasonably priced with the possibility
to change the provider). I've had my share of vendor lock-in.
* Support for handling XML data as in- and output.
* Separation of web frontend logic and web frontend design.
* Ease of use is never bad. ;)

I'm looking forward to your suggestions.
Thanks
Arthur