With my parents being far away from where I leave (10 hour time difference), we keep in touch usually by using Skype or Google Talk. While this works great as I have my laptop around me at least 8 hours a day (Tablet PC with built-in mic), there are shortcomings with that and the reason for that is that these calls, while great in sound quality means that my parents and myself have to be close to a computer (with a broadband connection). With that said, the whole Internet calling can be divided in three parts:

PC to PC (Cost free)
The giants here are Skype and Google Talk in my opinion. MSN does not really come up to par in voice quality the few times I have tried.

Phone to Phone a.k.a Calling Cards (Not free)

Many options here to choose from (including buying calling cards from gas stations etc). One online option I have tried and I like is Jajah.com. Problem with JaJah is that you have to be around a PC to initiate the call (you give the number to the site, the site calls you then call the destination and connects the phone together). One thing good that is good about JaJah is that you can schedule a call which eliminates the need to be around a pc to initiate the call though, but that does not really solve the problem here. I am still looking for better and cheaper alternatives so feel free to drop a comment with tips.

PC to Phone (Not free)

Skype is a well known option here. But another option that my dad will not stop praising is internetcalls.com (both for it’s quality of voice and prices and it also works with SIP devices). I have not tried it myself, but will take my dad’s word for it.
Are you using better options for any of these three categories?