Concordancing, collocation and reference sources online

Hi Fellow ALLians
Can anyone recommend a good concordancing tool - free - that our students can keep opne in the background as they are writing.
I'm fast coming to the conclusion that a good online dictionary like the OED is more useful, as it also includes examples of words in context so that you can easily see how they collocate.
Any suggestions? What have you found works best for students?

Re: Concordancing, collocation and reference sources online

Hi Kate

Here are a few suggestions of places to start from English language teachers:

A Brisbane ESL teacher, Mike Smith, has recently developed a simple web tool that submits to multiple web sites at once. He also provides guidance on how to use each site.
(and he is still adding sites and help to the site, and refining the tool):

Leo Selivan has a useful list of ‘Essential lexical tools’ on his blog, with descriptions:

Rachael Roberts has blogged about ‘Some user-friendly concordance ideas’:

And there may be something useful in this summary of an #ELTchat from last year: ‘Using corpora in the classroom’: