If you're using xl2002+, maybe Insert|symbol would help.
Chip Pearson has an addin that may help (if you're using xl2k or lower).
http://www.cpearson.com/excel/download.htm
(look for Symbolizer and make sure you get the correct version)
Or even use Windows own CharMap:
(Windows start button|run|Charmap)
And if you're looking to find out what's already in a cell, Chip Pearson has a
very nice addin that can show you those codes:
http://www.cpearson.com/excel/CellView.htm