Dictionaries and references

Longman Dictionary of Contemporary English for Advanced Learners

Pearson Longman, 2009, fifth edition.
Includes a CD-rom which makes it very quick and easy to look up words and also has the following functions: a vocabulary activator which provides different words/phrases according to various shades of meaning of a word; a grammar reference and exercise section; a vocabulary exercise section; differences between British and American English; and a writing assistant which enables you to look up a word and find its collocations, synonyms and grammar just by holding your cursor over the word. 

Macmillan Collocations Dictionary

Although there are fewer collocations - some 4,500, this is perhaps a more practical collocations dictionary as it gives more notes on usage, tone and register than the Oxford Collocations Dictionary. 

Oxford Advanced Learners Dictionary

Oxford University Press, 2010, eighth edition.
Includes a CD-rom featuring the very useful Oxford iWriter function which you can use as a template for your writing and to get guidance on different types of writing. 

Oxford Collocations Dictionary

Oxford University Press.
A more comprehensive list of 9,000 headwords and the collocations that are used together with the headword: nouns, adjectives, verbs, prepositions.

Practical English Usage

Michael Swan, Oxford University Press.
The best reference book for a huge variety of aspects of how English in the real world. Very comprehensive. 

Roget's Thesaurus

The classic synonym dictionary.

Free dictionary

Very comprehensive, accesses definitions from several other dictionaries.

Gyldendals Danish/English dictionaries

The largest Danish-English/English-Danish dictionary, also includes an online version of the Oxford monolingual dictionary.

KU Lex

The University of Copenhagen dictionary of university terminology: for university technical terms, both Danish-English and English-Danish.

Merriam Webster online dictionaries

Includes a dictionary, thesaurus (synonym dictionary) and a medical dictionary.

One Look Dictionary Search

Enables you to look up a word in several dictionaries at once, or to look up words that begin or end with the keyword, or to find a list of words and phrases related to the keyword. 

Phrasal verbs dictionary  

Explains what phrasal verbs are, how to use them and has a comprehensive list of phrasal verbs with definitions and examples.

Collocations dictionary

Enables you to look up which words commonly co-occur.