Easily make suggestions for different search terms for mistyped words, based on any language’s dictionary or a dictionary based on the content of your site.
The second method is advised: every suggested alternative searchterm will always be found on your site, as it is based on *your* content. It indexes by default all the searchable custom fields. And it’s compatible with search add-ons like Low Search.
You can download it at http://devot-ee.com/add-ons/am-impact-search-suggest