I think this is very difficult...
I want to give the user the possibility to insert a city of world and see last earthquakes around it.
The problem is how create an input list with all cities.

In my form the user must before insert the country:
http://jsfiddle.net/Dimcho/LUZvS/

<div class=datalist-holder>

    <input list=country name=country class=datalist-input />

    <datalist id=country>

        <option value=Afghanistan />

        <option value=Albania />

        <option value=Algeria />

        <option value=American Samoa />

        <option value=Andorra />

        //...

        //...

    </datalist>

 </div>

and this jsfiddle works very well...

but to insert the city it's a big problem, how is possible ?
How can i find good database with all cities of world with its latitude, longitude and name of city (with region/province) ?

Anyway i can't insert all cities in my page so I had thought to load a single file with all cities of inserted country using javascript.

Is a good idea?

I would like a lot of advice, the important thing are solutions that do not slow down the code and the page. The performances are very important.

Thanks a lot and sorry for my english