HTML Drag and Drop Multiple Upload - http://www.appelsiini.net/2009/10/html5-drag-and-drop-multiple-file-upload

index.js

/* Cannot use $.bind() since jQuery does not normalize native events. */
$('#dropzone').get(0).addEventListener('drop', upload, false);

function upload(event) {
    
    var data = event.dataTransfer;

    var boundary = '------multipartformboundary' + (new Date).getTime();
    var dashdash = '--';
    var crlf     = '\r\n';

    /* Build RFC2388 string. */
    var builder = '';

    builder += dashdash;
    builder += boundary;
    builder += crlf;
    
    var xhr = new XMLHttpRequest();
    
    /* For each dropped file. */
    for (var i = 0; i < data.files.length; i++) {
        var file = data.files[i];

        /* Generate headers. */            
        builder += 'Content-Disposition: form-data; name="user_file[]"';
        if (file.fileName) {
          builder += '; filename="' + file.fileName + '"';
        }
        builder += crlf;

        builder += 'Content-Type: application/octet-stream';
        builder += crlf;
        builder += crlf; 

        /* Append binary data. */
        builder += file.getAsBinary();
        builder += crlf;

        /* Write boundary. */
        builder += dashdash;
        builder += boundary;
        builder += crlf;
    }
    
    /* Mark end of the request. */
    builder += dashdash;
    builder += boundary;
    builder += dashdash;
    builder += crlf;

    xhr.open("POST", "upload.php", true);
    xhr.setRequestHeader('content-type', 'multipart/form-data; boundary=' 
        + boundary);
    xhr.sendAsBinary(builder);        
    
    xhr.onload = function(event) { 
        /* If we got an error display it. */
        if (xhr.responseText) {
            alert(xhr.responseText);
        }
        $("#dropzone").load("list.php?random=" +  (new Date).getTime());
    };
    
    /* Prevent FireFox opening the dragged file. */
    event.stopPropagation();
    
}

index.php

<?php

$error_message[0] = "Unknown problem with upload.";
$error_message[1] = "Uploaded file too large (load_max_filesize).";
$error_message[2] = "Uploaded file too large (MAX_FILE_SIZE).";
$error_message[3] = "File was only partially uploaded.";
$error_message[4] = "Choose a file to upload.";

$upload_dir  = './tmp/';
$num_files = count($_FILES['user_file']['name']);

for ($i=0; $i < $num_files; $i++) {
    $upload_file = $upload_dir . basename($_FILES['user_file']['name'][$i]);

    if (!preg_match("/(gif|jpg|jpeg|png)$/",$_FILES['user_file']['name'][$i])) {
        print "I asked for an image...";
    } else {
        if (is_uploaded_file($_FILES['user_file']['tmp_name'][$i])) {
            if (move_uploaded_file($_FILES['user_file']['tmp_name'][$i], 
				$upload_file)) {
                /* Great success... */
            } else {
                print $error_message[$_FILES['user_file']['error'][$i]];
            }
        } else {
            print $error_message[$_FILES['user_file']['error'][$i]];
        }    
    }
}
?>