The Mystery Of The Aleph

This article from the "Washington Post" covers the development of the concept of infinity, from the fifth to the second century B.C., and includes the main findings of Archimedes and the Pythagorean school. [Requires free registration.]
http://www.washingtonpost.com/wp-srv/style/longterm/books/chap1/mysteryaleph.htm

MacTutor History of Mathematics

An extensive and searchable archive covering famous people and concepts, as well as describing the development of mathematics in various cultures.
http://www-groups.dcs.st-and.ac.uk/~history/

History of Mathematics

An overview of the subject and a famous 1900 speech describing the main mathematical problems. Includes a chronological list of mathematicians and their work.
http://aleph0.clarku.edu/~djoyce/mathhist/

Famous Problems in the History of Mathematics

Describes what mathematicians have worked on, from ancient times to the present. Includes problems suitable for middle school and high school math students, with links to solutions.
http://mathforum.org/isaac/mathhist.html

Ancient Geometry

Presenting an overview from ancient times to the present day, including descriptions of the discovery of pi and the origins of trigonometry.
http://members.aol.com/bbyars1/contents.html

The History of Mathematicians and Physicists

Outlines a Webquest for studying the history of contributions to both these fields, and includes resources for solving the task.
http://education.nmsu.edu/webquest/wq/math/mathpyswq.htm

History of Mathematics

Describes the earliest known uses of common words and symbols, as well as explaining some of the ambiguous terms that might be encountered at high school level.
http://members.aol.com/jeff570/

Babylonian Math

This site was created to help people understand the Babylonian math system better.
http://www.angelfire.com/il2/babylonianmath

Why Do We Study Calculus?

Explains, in everyday language, the developments in astronomy, math, and physics that contributed to the discovery of differential calculus and its relationship to area formulas.
http://math.vanderbilt.edu/~schectex/courses/whystudy.html

Egyptian Mathematical Papyri

Includes a description of each written document, as well as some sample problems from the Rhind, Moscow and other papyri. These ancient written works were created between 1900 and 1800 BC.
http://www.math.buffalo.edu/mad/Ancient-Africa/mad_ancient_egyptpapyrus.html

Arabic Mathematics: Forgotten Brilliance?

Explains contributions of Arabian mathematicians by translating early Greek texts, developing early algebraic ideas, number theory and astronomical calculations. Includes information about key people during this time period.
http://www-history.mcs.st-and.ac.uk/history/HistTopics/Arabic_mathematics.html

Earliest Uses of Mathematical Symbols

Discusses first known appearances of common expressions, such as operations, variables and trigonometric functions.
http://members.aol.com/jeff570/mathsym.html

History of Math Notes

Timeline for Babylonian, Egyptian, Greek, Chinese, Indian, Arabic, and European mathematical achievements. Includes summary of influences by important people in the field.
http://www.math.sfu.ca/histmath/math380notes/math380.html

History of Mathematics in Africa

Explains the early development of mathematical concepts in astronomical calculations, number systems, calendars and climate studies.
http://www.saxakali.com/COLOR_ASP/historymaf.htm

Mesopotamian Mathematics

Discusses the development of numbers, addition tables, exercise problems and solutions for quadratic equations in one of the oldest known civilizations. Covers the period from 8000 B.C. to 364 A.D.
http://it.stlawu.edu/~dmelvill/mesomath/

Mathematics History

Traces the development of math throughout the ages. Also includes biographies of famous mathematicians.
http://library.thinkquest.org/22584/

Math History Timeline - Pre-historic and Ancient Times

La Hababra high school page includes dates related to important developments in the field of mathematics, which occurred from approximately 30,000 B.C. to 500 A.D. Features an accompanying timeline for general historic events and photos.
http://lahabra.seniorhigh.net/pages/teachers/pages/math/timeline/MpreAndAncient.html

Maths is Good for You

Contains information on famous mathematicians, theorems, and topics.
http://www.mathsisgoodforyou.com/