Dialwise.ie is the best that I know of. No subscription or buying minutes etc. To landlines worldwide is dirt cheap, you dial 1890 99 0505, then you get a ringtone, then you dial your number. It is the cost of the 1890 you are paying, ie:
Mo-Fr 6pm/8am: 1.26 cent per min
Mo-Fr 8am/6pm: 4.92 cent per min
That is for nothing. It is billed on your monthly bill.
They also have rates for mobiles, still pretty cheap, eg Australia:
Mo-Fr 6pm/8am: 4.92 cent per min
Mo-Fr 8am/6pm: 8.17 cent per min
I dont like Skype, you often get very poor quality even when both ends are on a good connection.