• Open /Applications/Automator, create a new Service
• “Service receives selected files or folders in Finder
• Add a “Run AppleScript” action:

on run {input, parameters}
	set the clipboard to (posix path of input)
end run

• Save as Copy Path (or whatever you like)
• Open Systerm Preferences > Keyboard > Shortcuts > App Shortcuts
• Add a new one > Application: Finder, Menu Title: Copy Path (or whatever you saved it as), shortcut Ctrl-Cmd-C (or whataver you like)

Update: You can now do this directly in the Finder with Alt+Cmd+C