You can turn off diagnostics reporting: Choose Apple >System Preferences, click Security & Privacy, and then click Privacy. Deselect “Send diagnostic and usage data to Apple.”
You already found iCloud, but you can also turn off automatic updates in the App Store section of System Preferences.
And afterwards, install Little Snitch, a firewall that reports outgoing connections. If you don't want to spend money on that, open the commandline and type "man netstat" to find out about the netstat command.
It's a pretty interesting project -- an OS X installation that does not send traffic unless specifically user-initiated.