I think the title is explanatory enough:) What are the best books for development in SharePoint 2013? These advices will be helpful for those will not attend any SharePoint 2013 development training.
All the books that I'm aware of are at this time of writing not yet available (unless in draft mode from some publisher).
In the meantime, MSDN / Technet is filled with really good content with some outstanding training from Ignite (for the Preview release) really handy to get an extensive overview of anything new.
IT Pro SP2013 IT Pro Home - http://technet.microsoft.com/en-us/sharepoint/fp142366 Ignite Content - http://technet.microsoft.com/en-us/sharepoint/fp123606
Developer SP2013 Developer Home - http://msdn.microsoft.com/en-us/sharepoint/ Ignite Content - http://msdn.microsoft.com/en-US/sharepoint/fp123633
After that, you should grab the conference (eg : from Las Vegas or from Amsterdam recently) materials to go deeper into specific points.
Finally you have all the regular MVP / MCTS and the community which are already blogging a lot regarding the 2013 plateform.
So while in my opinion there is no "real meat" book available, you have plenty of ressource to start learning !
Edit : trusting Amazon as a good source : http://www.amazon.com/s/ref=sr_nr_i_0?rh=k%3A%22SharePoint+2013%22%2Ci%3Astripbooks&keywords=%22SharePoint+2013%22&ie=UTF8&qid=1355157243 all (except a few self published how to) are expected from late february / march / april 2013.