By simply replacing 4 files you can completely alter how the dock looks. This looks much nicer than the original leopard dock and it makes it a bit easier to see which applications are running.

Navigate to /System/Library/CoreServices
Right-click on Dock and ‘show package contents.
Navigate to /Contents/Resources/

Back up:

scurve-l.png
scurve-m.png
scurve-sm.png
scurve-xl.png

Then, replace them with these files.