ONLINE CONCORDANCER - http://www.lextutor.ca/concordancers/concord_e.html

CORPORA IN ELT; CORPORA IDEAS - http://www.hltmag.co.uk/ (go to "previous editions"-->"view by categories"-->"corpora ideas")

plus ...

Concordancing (Anna Mirowska-Przybył, IOU)

Corpus Concordance Sampler

The British National Corpus example online

A Ten-step Introduction to Concordancing through the Collins Cobuild Corpus Concordance Sampler