We have had lively discussions on solo diving on wetpixel in 2003 and 2007, including comments that PADI abhors solo diving like nature abhors a vacuum. So I was surprised to find out that PADI has recently introduced an official solo diving specialty course, although they call it the self-reliant diver course. Ironically, I found out while taking the SDI solo diver course. I can't comment on which course is better as I don't know much about PADI's offering, but did like the SDI course, especially the in-water part of it. The good thing about the PADI course is that it may make dive operators more willing to allow divers with the appropriate training, equipment and demonstrated skills to go it alone.
Bart