www.voipubuster.com is working reasonably well if you use their own application but not so well if you try to use Xlite or an alternative.  www.cheapvoip.com is better but gives you free calls to UK,Ireland and Holland. www.call18866.com also provides a VOIP service.  These are all in fact provided by Finarea SA.

www.voipuser.org is an interesting 'VOIP community' site that uses inbound minutes to fund outbound calls.

I agree. Skype is about the best there is at the moment. I speak to my mother UK to Uk and my brother in Germay at the same time. It's crystal clear and free.
They also have awesome rates to dial anywhere in the world, you just buy credit and dial then talk to any number in the world through your pc.