Stripes is without a doubt the best and easiest java framework I've ever had the pleasure of using. To address each of your reqs:
Be MVC based.
MVC is sort-of in the eye of the beholder--at least, this depends heavily on how you design your code structure. But yes, it's quite simple to use an MVC project structure with Stripes.
Have minimal if any configuration
This is where Stripes shines. To get up and running you need only to put a few lines in your web.xml. Everything else is automagically wired-up. The beauty of Stripes is that everything can be easily overridden if you so desire.
Have an easy to use ORM
Stripernate is a popular extension to the framework that, again, works automagically.
Have decent session management
As simple as a @Session annotation on the field. Or you can persist the entire ActionBean in the session if you want. Stripes has built-in support for Wizards, so you don't have to concern yourself about preserving state across requests.
Be easy to pickup
This is Stripes' strongest suit. Not to mention, the Wiki is incredibly well-documented.
In addition, Stripes has built-in support for layout templates, localization, AJAX, and a bunch of other stuff. And unlike some frameworks that require dozens of gigantic JARs (cough... Tapestry), the entire framework is a single JAR that weighs in at less than 500 KB.
