What out-of-print books would you like to see re-printed? It's excellent news that the LMS are to re-publish Cassels & Fröhlich.  There are many other excellent mathematics books which are just about impossible (or at least very expensive) to get hold of, though this problem seems to be getting a bit better with some texts being printed on demand.

Which book(s) would you most like to see re-published?

A couple of comments:
Perhaps nobody under 30 actually reads real books made from trees any more, but personally I find it more convenient to refer to a paper copy, to the extent that  I will happily buy a copy of something which is available free on-line (like SGA 1 and 2, or Milne's Arithmetic Duality Theorems).
And of course there can be legal issues with re-publishing works - EGA & SGA seem to be a case in point at the moment.
Here are two to start off with:


*

*Manin, Cubic forms

*Grothendieck et al., Dix exposés sur la cohomologie des schémas
(not including Cassels & Fröhlich because I picked up a copy on Amazon a couple of years ago :-) )
 A: I'm REAL excited about this question,but I don't have the time right now to think about it enough to post a list. I was actually going to compile one for Dover this summer-a long one. But I'll think about it and try and post a few at this thread.Here's a few to get started:
Elements of Homotopy Theory by George Whitehead:A classic by the master and it would be a fantastic resource for classical homotopy theory from a geometrical standpoint that can serve as a foundation for the modern,high tech treatment via model categories.Why it's out of print baffles me.
Analysis And Solution of Partial Differential Equations by Robert L.Street:There are so few good undergraduate textbooks on this subject and a nice inexpensive reissue of this book would go a long way towards assisting this situation.Wonderful discussion and lots of nice examples.
Notes on Differential Geometry by Noel J.Hicks: An absolute classic and it needs to be brought back for a new generation of graduate students-after being proofread carefully,of course.Graduate students learning differential geometry will wonder why people have been hiding it from them.
The Foundations of Geometry by K.Borsuk and Smilew:A lost classic on axiomatic treatment of the classical plane geometries from a modern standpoint.Another book that baffles me why it's out of print.
There-that'll get you guys started. I actually hope to post the full list at my blog this summer. I'll let you guys know when it's up for the world to see.
A: Hans Rademacher "Topics in analytic number Theory" 
Lester Ford "Differential Equations"
F. Hirzebruch "Topological Methods in Algebraic Geometry"
M. Greenberg "Lectures on Algebraic Topology"
M. Atiyah, I. MacDonald "Introduction to Commutative Algebra"
A: *

*Topology by James Dugundji

*General Topology by Ryszard Engelking

*Topology - Volumes I and II by Kazimierz Kuratowski

A: *

*Dixmier, C$^*$-algebras or Les C$^*$-algèbres et leurs représentations

*Dixmier, von Neumann algebras or Les algèbres d'opérateurs dans l'espace hilbertien: algèbres de von Neumann

*Pedersen, C$^*$-algebras and their automorphism groups
A: "Essays In Group Theory" edited by S.M. Gersten, which in particular contains Gromov's paper "Hyperbolic Groups".
A: "Topologie Algébrique et Théorie des Faisceaux," by Roger Godement.  The classic reference on sheaf theory. The edition I'm reading right now (checked out from the library) is beginning to fall apart, and it's really making my eyes water.
A: The situation with Séminaire de géométrie algébrique du Bois-Marie (SGA) remains incredibly frustrating:

*

*12 out of 13 volumes (all except SGA 4½) had been unavailable for a long time,

*until Société Mathématique de France issued new editions of SGA 1 and 2 in the early 00s and SGA 3 (parts I and III only ― part II appears missing) in 2011,

*but now SGA 1 and SGA 2 are already taken out of print again!

These books are still the backbone for serious theoretical work in algebraic geometry. I cite them in most papers I write.

By contrast, as I learned from this post, all 8 volumes of Éléments de géométrie algébrique (EGA) can be purchased directly from the IHES library for a very modest price!
A: Mathematics Made Difficult, by Carl Linderholm. A great underground classic.
A: I would very much like to see Cornell and Silverman's Arithmetic Geometry republished. May I ask for a reference regarding the republication of Cassels and Fröhlich? I hadn't heard about this, and it's also at the top of my list for out-of-print books that should be republished.
A: "Homotopic topology" by Fomenko and Fuks, the English version. I already mentioned it here.
A: Adeles and Algebraic Groups by A.Weil
A: I don't know much about the book, since it is out of print and i am young, but Stong's Notes on Cobordism Theory.
A: Associative Algebras, by Richard S. Pierce.  Check out the ridiculous Amazon page for this:
http://www.amazon.com/gp/offer-listing/0387906932/ref=sr_1_1_olp?ie=UTF8&qid=1273632391&sr=8-1&condition=new
A: 'Etale Cohomology' by Gunter Tamme (translated by Manfred Kolster).
A: Kobayashi, "Differential geometry of complex vector bundles"
A: I've heard and read good things about "Mathematics, Form and Function" by Saunders Mac Lane which is sadly out of print. Second hand copies are scarce and prohibitively expensive.
A: The whole Academic Press series on pure and applied mathematics contains a number of gems, including Mordell's work on Diophantine equations and Fuchs' work on infinite abelian groups. Unfortunately, it is out of print and used editions are usually horribly expensive. 
A: *

*Furstenberg's Recurrence in Ergodic Theory and Combinatorial Number Theory

*Dubins and Savage's How to Gamble If You Must: Inequalities for Stochastic Processes
A: "The Geometry of Moduli Spaces of Sheaves" by Huybrechts and Lehn. Thankfully, it seems that an updated edition is in the works.
A: "The Floer Memorial Volume." 
For anyone interested in instanton Floer homology, this book contains key articles by Floer, Donaldson, Braams, and others which aren't available anywhere else, the internet included (and which are still the sole references for certain proofs and ideas). My research has been held up for days, just due to this book being checked out. 
A: Murre's "Lectures on an introduction to Grothendieck's theory of the fundamental group".
A: Manifolds of differential mapping: P.W. Michor.  should be printed with latex and graphics...
A: H.R. Margolis, Spectra and the Steenrod Algebra.
This book was a big influence on my advisor, and I've been lucky enough to borrow and read his copy. It's basically impossible to find nowadays but is still an amazing treatment of this subject.
A: The following link may be relevant:
http://outofprintmath.blogspot.com/ - a blog devoted to trying to see which math books are in most dire need of reprinting.
Also 
http://terrytao.wordpress.com/2008/07/16/timothy-chow-out-of-print-math-books/  For some backround info about this site.
A: Perhaps we should be asking why excellent books are out of print. By what mechanisms can they be brought back to life?  Can we learn from any successful campaigns?
For me: Lectures on the theory of functions of a complex variable Vols I & II
published in the 1960's by Noordhoff. A beautiful book authored by Sansone &
Gerretsen.
A: The Complex Analytic Theory of Teichmüller Spaces, by Subhashis Nag. ISBN:0471627739.
It is for more than $500 on Amazon!!
A: Would also like to suggest to the list "Local Class Field Theory" by Iwasawa. 
A: Differential Galois Theory by J.-F. Pommaret.
This is the first book on nonlinear differential Galois theory. (Second hand copies only seem to be available at ridiculous prices.)
A: Philip F Reichmeider, The Equivalence of Some Combinatorial Matching Theorems. A fine little book about Hall's Marriage Theorem, Konig's Theorem, Dilworth's Theorem, Ford-Fulkerson, and so on, and the relations among them. 
A: The three volume of “Connections, Curvature and Cohomology”
A: Élie Cartan, Œuvres complètes. See how expensive and rare used copies are.
A: Methods of representation theory (Vol 1+2) by Curtis and Reiner. It's a shame that this is out of print!
A: After a quick pop over to my Amazon wish list, the following 4 have been pretty unattainable to me for as long as I've been looking:
Galois Cohomology of Algebraic Number Fields, by Haberland
Class Field Theory, by Neukirch
Arithmetic Geometry, by Cornell et al.
Number Theory, by Borevich and Shafarevich
(So if anyone has one they want to get rid of...)
A: Not likely to be a popular choice on MO, but I wish I could get a copy of Banach-Mazur Distances and Finite-Dimensional Operator Ideals by Tomczak-Jaegermann.
A: (1) "Algebraic groups and number theory" by Platonov and Rapinchuk
(2) "Spherical functions on a group of p-adic type" by Macdonald
(3) "Topological transformation groups" by Montgomery and Zippin
A: Sieradski's 'An Introduction to Topology and Homotopy' is my favorite introduction to the subject. 
A: For a long time, I wished the Hungarian translation of Knuth's The Art of Computer Programming volumes 1-3 would be reprinted.  I got lucky and I now have a used copy, but I guess it might still help others.
A: Complex Analysis, by E.T. Copson. Very beautiful book on a beautiful subject. Sad that it is out of print.
A: The algebra of random variables by Melvin Dale Springer  (Wiley series in probability and mathematical statistics) in 1979 is on offer used at amazon.com for prices starting at about 500$ ... 
