I have looked into reactive programming lately. Here are a few resources I've put together during my research.
The first resource is an introduction to the theory of actors from the horses mouth. Erik Meijer interviews Carl Hewitt, father of the actor model. They have fun and the explanation is clear and straightforward.
This presentation shows Jonas Bonér explaining the tenets of the Reactive Manifesto and how the Akka actor system adresses reactive programming.
Coursera has two courses that are relevant. The top link is about the Principles of Reactive Programming. Unfortunately the course has run and it has no future sessions scheduled yet, but it looks good. The other course is a "prereq" for the reactive course that teaches Scala.
Kresten Krab Thorup writes about how to think about actors when making actor systems.
A very nice practical write-up about using actors for parallell computing of a mandelbrot set. Well written and easy to understand.
Roland Kuhn is writing a promising book about Reactive Design Patterns. It is currently in the Manning Early Access Program but the first chapter that is an intro to reactive programming is freely available already.
Slideshare from Jonas Bonér. It isn't the same as watching the guy give the presentation but on the other hand you can get through the slides quicker.
The presentations from Scala Days 2014 are out on Parleys. There is a bunch of presentations on reactive programming which in Scala basically means actors.