Focus – a site I'm quickly growing to love – has a nice infographic on some of the key disruptive companies in the market today.
Personally, I would add in Salesforce.com who I still think has one of the most disruptive platforms in B2B (disclosure: I've worked with Salesforce.com on their Social-Powered Enterprise content with Velocity Partners – but I rated them highly before that).
Click the image to see it full size.
;)