Apparently Photoshop's Bicubic smoother does a pretty good job and rivals onOne's Genuine Fractals up to a certain scale of enlargement. I have Genuine Fractals and it does an amazing job.
James, How large of an enlargement?
If you're working on a PC, Qimage is a great program for doing enlargements. I've found it does a wonderful job on prints up to 20 x 30 (might do them in a larger size but that is the limit of my printer). It has an outstanding sharpening routine that takes all the work out of output sharpening.
Thanks all for your input. My intention is to enlarge a photo, then give it to a commercial printer for poster size printing. I realize that the commercial printer can do the same thing from a high resolution jpg, but think I can create a better result by enlarging beforehand.