defaults write com.apple.dock no-glass -boolean YES; killall Dock;
Great thanks!Dockulicious
http://www.dockulicious.com/docks/index/page:1/
and their dock app
http://www.dockulicious.com/download
This app requires the dock style be zipped, and will replace everything in the dock including indicators and divider
LeopardDocks
http://www.leoparddocks.com/
and their dock app
http://www.leoparddocks.com/download/ChangeDock.zip
This app doesn't need a dock style zipped, but will only replace the scurves.
Fun stuff.
Or to turn off 3D dock, in terminal
Change to NO to get 3D backCode:defaults write com.apple.dock no-glass -boolean YES; killall Dock;
(Caution when using terminal)