I've read SPIN selling and now reading Challenger Sales.

SPIN is much easier to read, know and understand while I found Challenger Sales a lot difficult to follow and put into practice.

Challenger Sale's major premise is the assumption that SPIN selling doesn't work anymore for some reason because of the 2008 recession. I'm not sure how true this assumption is but I'll leave this up for the real sales people.

I'm interested in hacking enterprise sales. ANother HN user's blog on the subject here is excellent as well: http://doanhdo.blogspot.ca/