populating Drop down with items frmo server.

[andreasblixt]

The cleanest approach by far (in my opinion) is to only have PHP generate a delimited list of the options, and then programmatically add them to the list with JavaScript. You could for example separate items with commas:

// Output comma-delimited list of items (assuming $items is an array.)
die(implode(",", $items)); 

Then in JavaScript you would add it programmatically:

var items = request.responseText.split(",");
for (var i = 0; i < items.length; i++) {
    // ...
}

If you want it to be true AJAX (Asynchronous JavaScript and XML), you could generate an XML response (and use the responseXml property):

<?xml version="1.0"?>
<items>
  <item>Item One</item>
  <item>Item Two</item>
</items>

In any case, I don't like the idea of generating HTML in one application and just blindly inserting it into another (using innerHTML.)