The Mythical Man-Month : Essays on Software Engineering by Fredrick P. Brooks, Jr. - one of the first books on software management by the team leader of the OS/360 IBM Mainframe operating system. Despite the fact that it was originally written in 1975 , it still contains many useful insights on software engineering.
The Cathedral and the Bazaar aims to explain how the problems raised by this book can be easily resolved.
Open Sources: Voices from the Open Source Revolution
This book is available online and gives the opinions of many of the most prominent leaders of the Free Software and Open Source world.