Onsuite.com is my favorable long distance provider. I have been using it service since July 2002 and am very happy about the service and the rate. I can call anywhere in the US for 2.5 cents/min. I can call China even cheaper at 2.4 cents/min.
During the year there was a huge up-and-down of calling rate to China, and I found onesuite.com rate is the cheapest most of the time. Also, I'm very happy to be able to track my long-distance phone transactions in real time via web.