Go
There are estimated to be about 
possible positions on a 
board (Flammenkamp).The number of 
-move Go games are 1, 362, 130683, 47046242, ... (Sloane's A007565).
References
Beeler, M.; Gosper, R. W.; and Schroeppel, R. HAKMEM. Cambridge, MA: MIT Artificial Intelligence Laboratory, Memo AIM-239, Item 96, Feb. 1972. Flammenkamp, A. ``A Short, Concise Ruleset of Go.'' http://www.uni-bielefeld.de/~achim/gorules.html. Kraitchik, M. ``Go.'' §12.4 in Mathematical Recreations. New York: W. W. Norton, pp. 279-280, 1942. Sloane, N. J. A. SequenceA007565/M5447in ``An On-Line Version of the Encyclopedia of Integer Sequences.''http://www.research.att.com/~njas/sequences/eisonline.html and Sloane, N. J. A. and Plouffe, S.The Encyclopedia of Integer Sequences. San Diego: Academic Press, 1995.
- Snake Eyes
- Snake Oil Method
- Snake Polyiamond
- Snedecor's F-Distribution
- Snellius-Pothenot Problem
- Snowflake
- Snub Cube
- Snub Cuboctahedron
- Snub Disphenoid
- Snub Dodecadodecahedron
- Snub Dodecahedron
- Snub Icosidodecadodecahedron
- Snub Icosidodecahedron
- Snub Polyhedron
- Snub Square Antiprism
- Soap Bubble
- Soccer Ball
- Sociable Numbers
- Social Choice Theory
- Socrates' Paradox
- Soddy Circles
- Soddy Line
- Soddy Points
- Soddy's Hexlet
- Sofa Constant