JS library (with drag n drop) compatible with iOS and regular browsers
Here's two built in jQuery:
http://www.stevefenton.co.uk/cmsfiles/assets/File/mobiledragdrop.html
http://code.google.com/p/jquery-ui-for-ipad-and-iphone/
There is also the jquery mobile framework (which does not have drag and drop nativly):http://jquerymobile.com/
I'm a big fan of Sencha Touch.
Here's there drag and drop demo - http://dev.sencha.com/deploy/touch/examples/dragdrop/.
Note: Tested on my iPhone 4 in Safari.
JQuery Mobile is trying to support a large variety of platforms
And here is a specific plugins for Drag and Drop