In my academic research on numerals, ancient numeracy, and non-Western mathematics (ethnomathematics), I have come across a range of useful online references that may be of interest to specialists and non-specialists alike. If you are interested in my research specifically, you should consult my curriculum vitae which is available online and which has abstracts of my publications and scholarly presentations. If you're looking for some useful books on the subject, check out my numeration books page.
A learning module designed at the University of Wolverhampton for presenting social and historical aspects of mathematics to university students. While some of the information on the site is rather outdated or incorrect, it is nonetheless a valuable resource for those looking for an introduction to the topic.
Gary Urton and Carrie Brezine have put together this remarkable resource of information concerning the Inka khipu (or quipu) knot-records used in the Andes mountains region, most importantly describing the physical structure and composition of these fascinating notational artifacts. Very highly recommended!
Perhaps the best general introduction to the history of mathematics available on the Internet, hosted at the University of St. Andrew's in Scotland. In addition to an enormous collection of biographies of ancient and modern mathematicians, the site pays special attention to the mathematics and allied practices of ancient and non-Western societies, including numeration.
The superlative email discussion list on the history of mathematics. If you are investigating a specific question regarding numbers or numeration, the well-informed scholars and amateurs on this list may well be able to help you.
Historian of mathematics Duncan Melville at St. Lawrence University has produced this very useful introduction to ancient Mesopotamian (Sumerian, Akkadian, and Babylonian) numeration, metrology, and mathematics.
Mark Rosenfelder has compiled this tremendous page listing the numeral words for 1 through 10 in virtually all the world's languages for which there is sufficient data, organized by language family to allow for informal lexical comparison. Highly recommended.
A collection of the number words for 67 languages. While covering far fewer languages than the previous link, it has the advantage of providing the entirety of the numeral systems, allowing you to examine the base and structure of the systems much more readily.
An academic research unit run by Carol Justus at the University of Texas-Austin, oriented towards producing research on number words and number symbols. Strongly recommended for specialists and those interested in advanced reading on the subject.
A German-language resource on the history of ancient and non-Western numerical notations, designed primarily for senior students and other non-specialists. Useful although some of the information is considerably dated.