Get a Div Value in JQuery

I have a page containing the following div element:

<div id="myDiv" class="myDivClass" style="">Some Value</div>

How would I retrieve the value ("Some Value") either through JQuery or through standard JS? I tried:

var mb = document.getElementById("myDiv");

But the debugger console shows "mb is null". Just wondering how to retrieve this value.

---- UPDATE ---- When I try the suggestion I get: $ is not a function

This is part of a JQuery event handler where I am trying to read the value when I click a button. The handler function is working but it can't interpret the jQuery value it seems:

jQuery('#gregsButton').click(function() { 
   var mb = $('#myDiv').text();
   alert("Value of div is: " + mb.value); 
});