How about the following?
$("div.right").each(function(i){
$(this).prepend((i + 1) + ". ");
});
UPDATE:
Here is one way that should work.
"number" is a custom element (it can be anything you want) that will/should be ignored by browsers.
$("div.right").each(function(i){
$(this).find("number").remove().end()
.prepend("<number>(i + 1) + ". </number>");
});
OR use the following which is probably a little slower but semantically correct...
$("div.right").each(function(i){
$(this).find("span.number").remove().end()
.prepend("<span class='number'>" + (i + 1) + ". </span>");
});
OR an even better way would be to prepend span.number before your first drag:
$(function(){ // document ready...
// caching the "numbers" will only work if you use the DOM
// for updating div position (like jQuery's "append()", "prepend()", "before()", and "after()") and not "innerHTML" or "html()"
var numbers = $("div.right").each(function(i){
$(this).prepend("<span class='number'>" + (++i) + "</span>. ");
}).find("span.number");
function dragEnd(){
// do your drag end stuff here...
numbers.each(function(i){
this.innerHTML = ++i;
});
)};
});