You will need to be logged in to preview the different styles, I would suggest right clicking each one and opening in new window so you can keep this post open.
EDIT*****************
If the styles do not show for you, they can be previewed here

http://www.phpbb.com/styles/demo/3.0/
Happy voting.

Paul
Absolution
Afterburner
DarkFantasy
fisubice2
Frozen Phoenix
Glass softblue
hermes
milky way
Prosilver
rainbowpearll
Rock'n Roll
sabah
subAndreas08
subSilver2
twilightBB
we_clearblue (Current style)