I have been looking into this myself, but concrete implementation examples are rather sparse. 2 somewhat different approaches I've found are:
1) Using Behaviors and Attributes, with message-passing for communication, as described here:
http://www.gdcvault.com/play/1911/Theory-and-Practice-of-the
And in slightly more detail here (which also explains some advantages this method has over method #2):
http://www.pdf-archive.com/2012/01/08/entity-component-system/
With a short code example here:
http://gamedev.stackexchange.com/questions/22396/behavior-attribute-gamecomponent-architecture
2) The (more traditional?) method using regular old entities, components, and systems, as described here:
http://t-machine.org/index.php/2009/10/26/entity-systems-are-the-future-of-mmos-part-5/comment-page-2/#comments
This article focuses on using databases for MMOs, but it seems fairly easy to adapt to other types of games.
So far I'm leaning towards method 1, but I'm not quite sure how something like collision-detection would work. I think entities would have "hitbox" attributes which are used by "collides-with-Floor" (or "collides-with-enemy", etc) behaviors, but I dunno where the actual collision checks would go. Some kind of global behavior/system that the collision behaviors register themselves with?