Macroeconomics by N. Gregory Mankiw
Mankiw's text covers the field of macroeconomics accessibly and concisely, emphasising the relevance of both its classical roots and its practice at the beginning of the 21st century. It is updated to deal with the economic slowdown of 2001, due to the end of the stock market boom and the events of September 11, which has again put business cycle theory centre stage.