I've recently been using a service called VOIP Buster www.voipbuster.com
It offers free PC to landline calls to the following countries:
I have been using it to talk with the UK & USA & the quality has been very good. The people I called had no idea I was over the Internet & it sounded just like a regular call. There was a slight delay (no more than 1 second).
Calls to NZ are 1 Euro cent per minute but the quality is patchy & you would be better off using a calling card.
For International calls you can beat free & the quality to the UK & USA was better than I experienced with Skype.