Unlike most other IBO Diploma subjects, there are no officially supported/recommended IBO Computer Science textbooks. There are  a few semi-official textbooks are out there for the IB Computer Science 2014 syllabus. They are good resources, but perhaps a bit too technical for mid-range students and go into more depth than the curriculum explicitly requires. The revision guide is perhaps an easier to access textbook and worth getting.

Core Computer Science (that deals with the core syllabus, both SL and HL)

Advanced Computer Science (that deals with the extra sections for the HL syllabus)

IB Computer Science Study and Revision Guide (only for the core SL & HL syllabus)