A simple defaults command to tweak the Mac OS X menu bar to a solid color (instead of the yucky translucency) in Leopard:

sudo defaults write /System/Library/LaunchDaemons/com.apple.WindowServer 'EnvironmentVariables' -dict 'CI_NO_BACKGROUND_IMAGE' 1

Unfortunately, it breaks a cardinal rule, and (my) First Commandment of hacking Mac OS X:

Thou Shalt Not mess with anything under /System.