Flyr: A Flickr + Google Maps search tool - Here is a cool tool that allows you to search the Flickr image site for keywords in text, titles, tags and descriptions... pretty much anything that is searchable within the Flickr site! Dubbed "Flyr", your search results can be displayed as regular Flickr image results, plotted onto a Google Map or even opened up as an overlay in Google Earth.
Google Maps Mousewheel Zooming - This Greasemonkey script, once installed, will add support for mousewheel zooming on Google Maps. To reiterate, this is not a Firefox extension, rather a script that rides on top of Greasemonkey. Once you have installed Greasemonkey on your Firefox browser, open the script, go to the 'Tools' menu and click 'Install User Script'.
photo credit - Earthhopper
Hotel listings mashup releases plugin - Reservemy.com was one of the early hotel search sites to integrate Google Maps with their search results. They have released a Firefox plugin that allows you to search Reservemy.com's hotel listings straight from your Firefox browser.
Google Maps tool helps you find U.S. zip codes - This might be a re-post from a previous entry but you can always be reminded about this great Google Maps tool - click the U.S. map.. get the zip code. That easy.
Google Maps Tool Update: The previously mentioned "Areometer" tool has changed it's name to The Planimeter!