PHP 5, JSON from pecl cvs, Map Tile API and the Yui Connection Manager. Toss them in a bag and shake and you get something like this. Enter a city name, or even a pseudo-name like Philly or SFO and hit return. Each time you enter a new name you will get a map tile for that city.
It's not all that fancy, but it sure is easy to do:
With a slight tweak you can change it to make a nice geocode lookup field.
So, fire up your text editors and start writing some plugins for blog and forum packages and perhaps image gallery applications as well.