AJAX Suggestions is pretty much what you might have seen with Google Suggest.
The basic idea is, through AJAX, to give the user an immediate response to what they're typing and displaying the search results their input would generate.
AJAX Suggestions is an unobtrusive JavaScript to add that progressive enhancement to your web page, by the usage of two CSS class names to the desired input elements.
It could also be used, for instance, in an online e-mail application where you would want to check a name in a global address book and return the related matches, with the possibility to then adding them to the field element.
AJAX Suggestions is available either as stand-alone, or in conjunction with the DOMAssistant library.