Computer Algebra Nederland (CAN) - Coordinates the use of computer algebra in education and research. Research reports, newsletters and historical material.
SymbolicNet - Information centre for symbolic mathematical computation. Links to research and software.
Groebner Bases - Definitions and examples, with Java applet.
SIGSAM - ACM Special Interest Group in Symbolic and Algebraic Manipulation. Site has details of meetings, reports and other links.