'Don't Make Me Think' by Steve Krug
- This is probably the most straight-forward and basic books in the field. It will give you a foundational understanding of how to approach UX design.
'About Face' by Alan Cooper
- This one is my favorite. It is so unbelievably comprehensive and complete. It's very useful and after reading this you will be very informed. Alan Cooper is also one of the most important people in the field.
'The Inmates are Running the Asylum' by Alan Cooper
- Same author as above, this is a heavily cited book. This is actually the book where Cooper introduced the whole idea of 'personas' to the usability field. This book is basically for business people and technologists who don't understand the place of usability and why it's very important.
'The Design of Everyday Things' by Donald Norman
- This is one of those books that you are required to read in virtually any graduate program in usability or human factors (things may have changed now, but that certainly used to be the case and probably still is). This book isn't useful in a direct sense, but will give you a high level idea about how to approach design. I'm mostly putting it on the list for its historical importance.
'Designing with the Mind in Mind' by Jeff Johnson
- This book should be required reading for all UX practitioners in my opinion. Basically, the author takes the most relevant psychological principles and gives very specific real-world examples of how to apply them.
- I actually attended Steve Hoober's lecture at the 2014 UXPA annual conference. His talk was so incredible I looked him up and bought this book. It is hands-down the best book on mobile design I've ever come across, and I've read a lot of them. This book is a must have for anyone planning to do mobile design because the authors define patterns on a high enough level to not go obsolete easily. Very good book.
'Handbook of Usability Testing' by Jeffrey Rubin, Dana Chisnell and Jared Spool
- This book is a very straight-forward reference guide on usability testing. With your strong foundation in research, you'll easily understand everything in this book. So this will be very useful as a reference for the specific types of usability tests and research.