I think one of the best resources to learn Reason is the Reason's operation manual itself. It's free, in-depth, and made by the Reason producers. Other resources' relevance will depend on the Reason's current version and the literature that covers that version specifically. For example, the only third-party book that covers version 7 (the later version at the time of this answer) seems to be this one.
Propellerheads has its own learning shop and micro tutorials section.
A popular third-party Reason learning resource is Reason Experts.
You might want to widen your scope and learn sound design and music production outside of the Reason context, learn about them in general. This way you can apply this knowledge in Reason, FL Studio, Logic, Cubase, Live, and any other DAW, synth, sampler, tool.
Reason-specific material might dive too much into Reason particulars and not so much into synthesis and production. And that's a good thing if you want to be a Reason guru, but you might be more interested in synthesis and production than in the Reason system. If that's the case, you might want to learn about them directly and specifically.
There is an excellent sound design synthesis course in Coursera: Introduction to Sound Design. It's free, in-depth, with exams, forums, lectures, certification (not free), etc.
For general music production Berklee is offering a free introductory course in music production (through Coursera), that includes DAWs, effects, and even a little bit of sysnthesis. As the sound design course, this also includes lectures, forums, exams, certification (not free), etc.