twittervision
A mesmerising mashup of Twitter and Google Maps. I could watch this all day.
Related links
Where I Had My First Kiss . com - where was your first kiss?
Here's a mashup for ya: Google Maps meets young love.
Vitamin Features » Go forth and API
Cameron has written a great article on using APIs with Ajax. I love the idea of using .htaccess to fake a proxy and get around the same-site restriction.
overplot
This is an astoundingly brilliant mashup: Overheard in New York meets Google Maps. It's fan-bloody-tastic and remarkably fast for all the data it contains.
Google Maps API Documentation
Documentation for the new Google Maps API. Unlike most web services, this one is run entirely over JavaScript.