Free as in speech and beer (Darren Wershlter-Henry, 2002)
Interesting detailed romp through open source, peer-to-peer and its impacts on the economics of the web.
Rembrandts in the Attic (Rivette & Kline, 2000)
Excellent book about patent/IP strategies. Lots of good suggestions about patent audits and patent strategies. Summary statement: if landscape is uncharted territory, patents are the footprints along the frontier — valuable guides to those who know how to read (and use) them.
The Cathedral and the Bazaar (Eric Raymond, 1997)
Treatise on open source software (bazaar) development approach versus proprietary, company owned development (cathedral). Widely regarded as the seminal work on open source economic and philosophical foundations.