Online dictionaries

Danish:

• ordnet.dk: Den danske ordbog (moderne) & Ordbog over det danske sprog (1700-1950)

German:

• dict.leo.org: German to multiple languages. By Technischen Universität München.
• collinsdictionary.com: English-German-English.

Greek/Latin:

• philolog.us: Liddell-Scott-Jones, Slater and Lewis & Short. Interface for the lexicons at the Perseus Project.
• logeion.uchicago.edu: Another interface to LSJ and L&S.
• Whitaker’s Words: Morphological tool for latin. Hosted at the University of Notre Dame’s archives.

Hebrew:

• Gesenius: Genesius’ Hebrew and Chaldee Lexicon from 1846.

Swedish:

• sprogbro.org: Swedish-Danish.