Hi Ed,

There are a few dictionaries available online.

A Concise Dictionary of Old Icelandic by Geir T. Zoega
http://norse.ulver.com/ondict/zoega/index.html

...which is abridged from An Icelandic-English Dictionary by Richard Cleasby and Guðbrandur Vigfússon
http://www.ling.upenn.edu/~kurisuto/germanic/oi_cleasbyvigfusson_about.html#images

Ordbog over Det gamle norske Sprog by Johann Fritzner
http://www.dok.hf.uio.no/perl/search/search.cgi?appid=86&tabid=1275

Altnordisches Wörterbuch by Gerhard Köbler
http://www.koeblergerhard.de/anwbhinw.html

The Icelandic Online Dictionary is a dictionary of Modern Icelandic, but also useful to anyone interested in Old Norse. It's based on Íslensk-ensk orðabók / Concise Icelandic-English Dictionary by Sverrir Hólmarsson, Christopher Sanders and John Tucker
http://digicoll.library.wisc.edu/IcelOnline/Search.TEId.html

And for poetic vocabulary, there's Lexicon poeticum antiquæ linguæ septentrionalis: ordbog over det norsk-islandske skjaldesprog by Sveinbjörn Egilsson and Finnur Jónsson
http://www.septentrionalia.net/lex/index.php

And Eysteinn Björnsson's site Jormungrund
http://www.hi.is/~eybjorn/ugm/

For Old Swedish, Fornsvensk lexikalisk databas includes Ordbok Öfver svenska medeltids-språket by K.F. Söderwall, K.F. and Ordbok till Samlingen af Sweriges Gamla Lagar by C.J. Schlyter.
http://spraakdata.gu.se/sdw/

Old Danish, Ordbog til det ældre danske sprog by Otto Kalkar
http://www.hist.uib.no/kalkar/

There are more links in the links section of the Yahoo Groups Norse Course website, and here [ http://www.oe.eclipse.co.uk/nom/norselinks.htm ]. In particular, see the sections Dictionaries, Reference and Beginners. The last section includes sites with courses such as Old Norse Online [ http://www.utexas.edu/cola/depts/lrc/eieol/norol-TC-X.html ], which can also be used as a referrence grammar.