Pay for performance SEO quoting system. You don't usually know what you're getting w/ SEO because it's billed per hour or in the typical standard, pro, enterprise packages that work well for web apps but not keywords w/ different competition levels.
And, it feels like the interests of firms aren't always tied to their clients. "Of course we have a guarantee...you're on the first page (of Ask.com)!"
So, I'm working on a quoting / billing structure where customer payments are dictated by the ranking improvements. Feedback so far is good, but of course, it's a challenge.