Dictionaries

The One Look dictionary. Linked automatically to a range of general and specialist dictionaries, so you can just ask it about a word and it goes off and gets a range of opinion.
Dictionary.com
Webster's
Bibliomania
Merriam-Webster dictionary and thesaurus. Allows wildcard searching. Webster 'searchopolis'.
Wordsmyth dictionary
Weird words
Swedish/English dictionaries: Swe-Eng (1), Swe-Eng (2)
InterTran online translation

Writing and typesetting

inkspot.com section on grammar, style, editing
The Slot, for copy editing
"My Virtual Reference Desk." Section on grammar and style.
Lynch's grammar/style guide.
dictionary of printing terms
DTP site

Maps

Multimedia Mapping - UK maps

Other