I'm actually in the same position right now. I have a ton of black plether, about 5 yards worth. I initially bought it for a Freya(from chobits) costume. However I've been stuck with the excess for about 4 years now and I'm at the point that SOMETHING needs to be done with it. It's too bad that it's not a dark grey or it'd be perfect for a Lulu dress.
I'll be looking forward to good costume suggestions!