Most cost effective miners on the market at the moment?

[Darkhand]

Nothing is hitting ROI right now, but I'm wondering what the most efficient mining hardware is at the moment, from a cost per GH/s standpoint.  One of the group buys in the forums seems to be the best available anywhere right now, but I'm wondering if anyone else can point me in the right direction?

Thanks in advance and hello world!

EDIT:  This would be purely from a hardware/shipping price standpoint; lets assume electricity is free.