Since Symfony 1.x's admin generator, I found this kind of tool really useful to prototype applications, show something very quickly to customers etc.
Now for Symfony2, admin generator does not seems to be a priority (see here and here)
Django's admin generator seems very interesting...
Which web application admin generator (any language / technology) would you recommend (pros / cons)?
I can recommend CakePHP scaffolding, where you can also add admin routing. Nice for you is that you can stay on PHP, which you also used for Symphony. Be warned, you might get addicted to Cake ;)
Updated 2017
Agile UI (a successor of atk4.3) is an MIT based PHP UI Component library. It gives your application nice looking, consistent User Interface without you have to write any HTML and works with any PHP framework or application.
The reason I think this is better than a built-in generator:
To build a minimalistic application admin you only need 15 lines of PHP code:
Result:
something a lot more powerful for CakePHP is https://github.com/josegonzalez/cake_admin, little bit of a Django rip-off :)
Padrino has "Padrino Admin":
http://www.padrinorb.com/guides/padrino-admin
While not as popular as Rails, it's built around the excellent Sinatra DSL.
I like sprox, for Python. Although I have not found it particularly useful for production, it can help a lot in terms of prototyping and testing -- its simplicity is its strength here, enhancing Python's own strengths.
For Ruby on Rails: Here is some discussion on SO
But ActiveScaffold's home page at the moment is still talking about Rails 2.3, so you may want to read past the accepted answer and check the others to see if there are newer ones.
Rails Admin looks to be actively developed and has good pedigree (having been a Google Summer of Code project mentored by big names in the Rails community, so I'd start there if I were looking.