A growing collection of useful beginner & advanced level Rx materials.
https://gist.github.com/staltz/868e7e9bc2a7b8c1f754
A short, concise introduction to RxJava.
http://blog.danlew.net/2014/09/15/grokking-rxjava-part-1/
A serious of blogposts by Dan Lew on getting into RxJava, mainly in the context of Android.
https://github.com/mgp/effective-rxjava/tree/master/items
A list of useful Rx patterns, written by a developer who contributed to the Khan Academy Android app.
http://rxmarbles.com/
RxMarbles, a set of interactive diagrams explaining operators.
https://labs.ribot.co.uk/unit-testing-rxjava-6e9540d4a329#.qc1tqhuym
Quick introduction into unit testing Observables.
http://akarnokd.blogspot.hu/
David Karnok's blog about RxJava internals and various other Rx implementations. Massively useful to understand what's going on under the hood.
http://jakewharton.com/demystifying-rxjava-subscribers/
Jake Warthon's presentation, helping to understand RxJava Subscribers deeper.