I've seen a few old threads but no really basic or elegant solutions to Z-ordering in isometric games, so I figured I'd post what I came up with. Pardon if this is old news.
Anyways, here's your event right here:
<img src="http://i292.photobucket.com/albums/mm17/CookingwithMike/x1s/IsoZOrder_zps2de9d0be.png" border="0" />
Works great as long as origin points are consistent (bottom, ideally).