Google just published a list of community samples for their AJAX Search API. Currently there are only four samples listed -- but I'm sure there will be many more in the future. For a list of examples created by Google, check out the usage samples on their website.
The current list includes:
SuccessForce.com (Kingsley Joseph) - Integrated site search with slide-down animation. Also returns search results as you type and provides permanent links to search results, a common challenge with AJAX applications.
CCFotos Picture Reference Finder (Marcio S. Galli) - An image finder that does a site search and then returns thumbnail images associated with the webpages in the results.
Local Chat Gadget (Myself) - Google Gadget that let's you communicate with people in your community. Search for local businesses by using the "search" menu or by typing "/search "
Bilingual Search (H.K. Tang) - Enables search in two languages at the same time. Search results are returned for the user's keywords, as well as for those keywords translated into another language.