are you doing the one where you put one end of the barbell into the corner and put a bunch of weight on the other side? then, you grab the weighted end and swing it overhead?
if so, it's called many things, like a reverse barbell woodchopper, corner barbell twist, "the cornerstone", etc...
here's pavel's version which, i think, is standard.http://www.bodybuilding.com/fun/mm6.htm
or, you can do john davie's version (he's a respected strength trainer). what he does is when you do the twist, you take a big explosive step so that your outer foot becomes parallel to your inner foot in respect to the corner. in other words, your shoulders become perpendicular to the barbell.