You might be interested in the latest digital version of the Bosworth and Toller Old English Dictionary:

http://bosworth.ff.cuni.cz/

Ondřej Tichý, who maintains the site, is a friend of mine from the ISAS digital workshop last summer.

If you have used one of the other digital Bosworth and Tollers online, you will be happy to find this one has vastly greater search capabilities. For instance, you can used the advanced search to find all words that contain a particular root (I experience a brief period of euphoria when I search for 'mod'; that was a lie: I am still in that state of euphoria after a good hour), and you can search not only head words, but also definitions (helpful if you want to throw the occasional Old English into your Facebook status update).

I also posted a link on the MEGSE website, along with links to the other two digital alternatives:

http://megse.unm.edu/research/web.html