Devo Hats.

Rob at Cockeyed.com made these Devo hats for a Guitar Hero party, and posted step-by-step instructions. Link -via Everlasting Blort

I know this is really geeky. Someone posted the dimensions of the actual energy domes:

Dimensions for the Energy Domes (a.k.a. Flowerpot Hats) from Klilin:

This taken from a hat I caught at a concert:
material-thin plastic (vacu-formed), crimson red
form-4layer slightly conical crossection stack
base-9.3/8 tapers to 8.5/8 , 1.3/4 tall
next-7.1/2 tapers to 7 , 1.3/4 tall
next-5.5/8 tapers to 5 , 1.1/4 tall
top- 3.3/4 tapers to 3.1/2 , 3/4 tall
total height-5
logo on top-

EV
D O

letter size-3/4
top embossed 3/64
all dimensions in inches

By the way, the domes sold through the fan club are not the same as the ones actually worn by DEVO - DEVO's domes are bigger and don't have the letters on top.