Mankiw, N. Gregory;
Principles of Microeconomics;
The course text can be purchased as a bundle with the ECON105 text:
Mankiw, N., G. Bandyopadhyay, D. & Wooding, P. (2007). Principles of Macroeconomics in New Zealand. Australia: Thomson Learning.
This text bundle can be purchased for a combined student discount price that represents very good value and is a significant saving compared to buying both books separately. The bundle option has the advantage that students can sell one or both texts, though a good micro and macro principles text is a valuable addition to any student's collection especially if you plan to continue in economics, but is still very valuable even if you do not.
Some very readable books which give a very good introduction to the key ideas in economics include:
"New Ideas from Dead Economists" by Todd Buchholz
"The Undercover Economist" by Tim Harford
"Freakonomics" by Steven Levitt & Stephen Dubner