I know there are smaller systems out there, but this one would certainly pack a punch!!
http://www.anandtech.com/show/6267/intels-next-unit-of-computing-4x4-core-i3-systems-targeted-at-399
http://www.anandtech.com/show/6267/intels-next-unit-of-computing-4x4-core-i3-systems-targeted-at-399