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:

33 lines total which includes about 6 lines of PHP which consists mostly of building the URL to the map tile service. Then the Javascript which has a callback function to read the form values and make the backend GET request and a simple function to take the JSON response and add the map tile to the document. And finally the actual HTML form.

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.