What are the recent TCS books whose drafts are available online?
Several TCS books by Now Publishers can be found in drafts:


Foundations of Cryptography– A Primer by Oded Goldreich. This is a summarized version of his famous two-volume book on cryptography. (The draft of the two-volume version can be found in Robin's answer.)
Data Streams: Algorithms and Applications by S. Muthukrishnan.
Mathematical Aspects of Mixing Times in Markov Chains by Montenegro &amp; Tetali.
Pairwise Independence and Derandomization by Luby &amp; Widgerson.
Average-Case Complexity by Bogdanov &amp; Trevisan.
A Survey of Lower Bounds for Satisfiability and Related Problems by Melkebeek.
Algorithms and Data Structures for External Memory by Vitter.
Probabilistic Proof Systems: A Primer by Goldreich. Again, this is a summarized version of a part Goldreich's book Modern Cryptography, Probabilistic Proofs and Pseudorandomness.
The Design of Competitive Online Algorithms via a Primal-Dual Approach by Buchbinder &amp; Naor.
Spectral Algorithms by Kannan &amp; Vempala.
On the Power of Small-Depth Computation by Viola.
Algorithmic and Analysis Techniques in Property Testing by Ron.
Arithmetic Circuits: A Survey of Recent Results and Open Questions
by Amir Shpilka and Amir Yehudayoff (2010), Foundations and Trends® in Theoretical Computer Science: Vol. 5: No. 3–4, pp 207-388. http://dx.doi.org/10.1561/0400000039




In addition, drafts of several Springer books on "Information Security and Cryptography" can be found online:


Cryptography in Constant Parallel Time by Applebaum.
A Study of Statistical Zero-Knowledge Proofs by Vadhan.
Locally Decodable Codes and Private Information Retrieval Schemes by Yekhanin.
Concurrent Zero Knowledge by Rosen.