Biblical Hebrew
This is an excellent electronic dictionary as well as a excellent
program for comparing Bible texts. It has an abridged version of
Brown-Driver-Briggs which is useful for quick look ups. It also has
many Bible modules including multiple versions of the Hebrew Bible. Davar 3.0 is out of beta and even better than the previous 2.4.
This is a scanned copy of the 1910 edition. The PDF download is fully
searchable (except for the Hebrew text). Very important grammar.
This is a hint of good things to come for reference material on the web. The scanned version of GKC has been uploaded to Wikisource and its text is being edited collaboratively online. This is very exciting, and I am looking forward to a similar project moving forward for the BDB.
Scanned copy of the 1909 edition. Downloadable PDF. A index of every word in the BDB hyperlinked to its corresponding page is can be found here: aleph-mem and nun-tav.
Put up by the United Bible Society, although it is a work in progress, it has 3,000 entries already and allows you to see the word in context.
Parses and identifies every word form in the Hebrew Bible. Although this is not as useful in its current state, it can still be used in a pinch, and this version at the Internet Archive is a fine scan.
Pentateuch Studies
Provides a good listing of biblical laws by type and shows where they are found in the legal material of the Bible.
Aramaic
Aramaic lexicon that is fully searchable and up to date.
Put online by the Tyndale House. It is easy to jump to a letters and page headings, although the load speed is not the greatest.
Greek
Bibliography
This is an add-on for Firefox that captures bibliographic data from
webpages and allows you to keep a database of books, articles,
webpages, etc. It also has integration with Word and Openoffice in
order to create bibliographies in a document.