References
From Why start at x, y, z
A History of Mathematical Notations by Florian Cajori.
Jeff Miller maintains some pages on the earliest known uses of mathematical words and mathematical symbols, as well as a list of ambiguities encountered at high school.
Christian Lawson-Perfect collects links to papers, books and other stuff about notation and conventions.
Common Errors in College Mathematics
The Digital Library of Mathematical Functions' notation section
