I use a foam cannon with a cold water electric pressure washer. I've been doing it for a couple of years. I really like it.
Is it any better than the 2 bucket method? Nah, I don't think so. It takes more time, but it does add entertainment value. A buddy of mine and I started at the same time. He uses his cannon for EVERY wash. I use mine for almost every way... I'd stay 75% of the time.
I still actually do the 2 bucket method, though. Here's my process:
Rinse with the PW
Foam with the cannon
Wash with whatever media (either the Griot's wash pad or the Griot's boars hair brush) using the two bucket method
Rinse as I go, and then a final rinse without the pressure washer
As for soap, I've been using Chemical Guys Mr Pink. My buddy uses Chemical Guys Honeydew Snow Foam. They're both good, but I tend to lean towards the Mr. Pink. I find that it rinses a little easier and foams just as well.
I'm interested to see what others say, too. I'm always up for trying new products!