Disclaimer 1: Most of the stuff below is fairly heavy on the math side; I haven't found a nice introduction yet (if I keep on reading papers at my current speed, I might as well write one myself - unless BillSpight beats me to it once again). However http://mathworld.wolfram.com/GameTheory.html might provide a nice jump-off point, but it mostly deals with Classical Game Theory. Indeed, http://mathworld.wolfram.com/CombinatorialGameTheory.html seems devoid of interesting content.
Anyway, here are some places to look for stuff on Combinatorial Game Theory.
Online papers and other material:
- http://www.msri.org/publications/books/Book29/contents.html : most of the proceedings on a conference on Combinatorial Game Theory. Keep your Postscript viewer handy!
- http://www.math.berkeley.edu/~berlek/cgt/go.html : Elwyn Berlekamp's pages on Mathematical Go.
- http://www.math.berkeley.edu/~berlek/cgt/index.html : general pages by Elwyn Berlekamp on Combinatorial Game Theory.
- http://www1.ics.uci.edu/~eppstein/cgt/ : I haven't yet visited all the links, but this looks to me like a fairly comprehensive overview of pages related to Combinatorial Game Theory.
- http://www.cut-the-knot.com/Curriculum/index.html : A large compendium of games, puzzles and other stuff. Of special interest is (of course!) the Combinatorial Games section (229 to 241).
- http://www.gac.edu/~wolfe/ : David Wolfe's homepage, unreviewed as of yet.
- http://www.cs.ualberta.ca/~darse/Photos/Misc/cgt2000.html : group photo of the "Who's Who" in CGT (Berkeley, 2000).
- http://www.dumbo.ai.kyutech.ac.jp/~teigo/GoResearch/ : An index of papers on CGT and Go, some in Japanese
You can also search for "Surreal Numbers". This is also the title of the first book-length publication on this topic. It was written by Donald Knuth, and is sub-titled "How two ex-students turned on to pure mathematics and found total happiness". A review of the book is at http://www-cs-faculty.stanford.edu/~uno/sn.html . It is a whimsical book, and probably not the best introduction to the formalism that is now used. PDF, and other, versions are available via https://archive.org/details/SurrealNumbers .
- On Numbers And Games, by John Conway.
- Winning Ways, by Elwyn Berlekamp, John Conway, & Richard Guy.
- Mathematical Go, by Elwyn Berlekamp & David Wolfe.
- Combinatorial Game Theory by Aaron Siegel.
Disclaimer: I haven't read any of these books, but they seem pretty interesting to me...