Symbols.com  
   The world's largest online encyclopedia of graphic symbols, ranging from ideograms carved in mammoth teeth by Cro-Magnon men, to hobo signs and subway graffiti.
   http://www.symbols.com/

Dictionary of Symbolism  
   An online aid for exploring the meanings of symbols.
   http://www.umich.edu/~umfandsf/symbolismproject/symbolism.html/

Byzant - Esoteric Symbols  
   Discusses and illustrates a range of powerful and profound religious and esoteric symbols from both Western and Eastern traditions.
   http://www.byzant.com/symbols/

Review of Liungman's Dictionary of Symbols  
   Critical review by Seth Maislin, indexer and information architect.
   http://taxonomist.tripod.com/indexing/liungman.html

Blissymbol Dictionary  
   Comprehensive online dictionary of the Blissymbolics Language - used by linguistically disabled persons.
   http://www.symbols.net/blissymbolics/dictionary/