Also have a look at Hugin
http://hugin.sourceforge.net/as free open source you can be assured that it will continue to grow. I'm a little leery about PTGui as it appears to use unlicensed SIFT methods though the developer won't tell you the method to find matching points. However, PTGui's control point finder came out shortly after the SIFT clones came out. Basically all three are good programs but my conscience prevents me from asking to be paid for my panoramas if I'm not paying the developer of a new technology their due.