This isn't really a mod, but it's worth seeing if you haven't already. Dell's next-gen XPS case design.
http://www.gizmodo.com/gadgets/pcs/dell-xps-gaming-desktop-goes-radical-173364.php
http://www.dell.com/html/us/products/e3/index.html
http://www.gizmodo.com/gadgets/pcs/dell-xps-gaming-desktop-goes-radical-173364.php
http://www.dell.com/html/us/products/e3/index.html