Cambridge University Press have released this dictionary toolbar which you can add to your web browser. The search box appears at the top of your browser and links to http://dictionary.cambridge.org/dictionary/british/
The dictionary has meaning, common expressions with the word, examples of the how a word is used and you can listen to the pronunciation of the word. Very handy – especially when you are using a web-based email or writing on a social media site. Because this dictionary is designed for language learners, the definitions are easier than in a standard dictionary and the information about how a word is used is more explicit.
Cambridge University Press also have a range of iphone / Android dictionary apps – handy for those who need to look up a word on the go.