I've done a lot of web development in JSP/JSF, and lately quite a lot in ASP.NET.
I would like to learn one of the following: ruby/python/php, for quick and simple projects.
I don't really care which one it is as long as it meets following demands:
  - decent IDE (forget the notepad/pspad etc.), something with code completition (like eclipse/visual studio/netbeans)
  - it has to be able to run on windows (IDE and environment)
Thanks for suggestions
Cheers
PHP and use codecanyon.net to get things up and running quick. I got INRtracker.com running in under 2 months with what I just mentioned. 
If you're going to use php, then get wamp and then after you install it, restart your computer. Then click on the Wampserver short cut on your desktop to start it up and then click on the icon in the bottom right of your desktop (you might have to click a little arrow) and then click start all services, then you can put php files in your wamp/www folder (you should be able to get to that from your C drive). Then you test them by going to http://localhost/filename.php in your browser. Have fun dude!
From asp.net to python/ruby/php