Exalead- the search engine that thinks it's a concordancer

In addition to allowing you to specify words that must or must not be in the page, it also allows you to specify words that are preferable, but not compulsory, so you can do fuzzy searches.

From a languge perspective the proximity search, in which you can specify that the words must be close to each other is a promising feature that increases the ability of a search engine to act as a kind of concordancer. With it, you can search for words that go together and get examples where they are not immediately next to each other. It is, however, still in its infancy as you cannot set the number of words apart, but it is a good start and will doubtless be improved.

It has other interesting language features, including word stemming, so you can enter a word stem and get different form of the word; not just plurals, but also suffixes, including spelling changes. It also allows you to search using a 'phonetic' spelling if you're not sure of the correct way to spell a word. You can also search for words with missing letters (a.....dation = accommodation), like a wildcard search. Search engines are still a long way behind the really powerful concordancers like Variation in English Words and Phrases, which searches the British National Corpus and allows far more exact searches, including grammatical types, maximum number of words apart, type of text to search, etc. However, the speed at which search engines are developing suggests that there is a strong likelihood that they will soon be able to do much of what a concordancer can do with the benefits of an interface that users are familiar with and searching over a far wider database.