For software development - I favor books that are about good practices generally rather than books about particular languages which work well as references.

I usually recommend:

* Code Complete (Steve McConnell)

* The Pragmatic Programmer (Andrew Hunt and Dave Thomas)

* Clean Code and The Clean Coder (Robert Martin)

* The Mythical Man-Month (Fred Brooks)

* Test-Driven Development By Example (Kent Beck)

I also recommend blogs for more bite-sized knowledge. Jeff Atwood's blog at https://blog.codinghorror.com and Joel Spolsky's at https://www.joelonsoftware.com in particular have been helpful to me.