This is a place to list the landing pages with the best good conversion ratio.
- http://www.desk.com/
- http://www.shopify.com/
- http://visualwebsiteoptimizer.com/
- http://floatapp.com/
- http://mailchimp.com/
- https://bitbucket.org/
- https://sketchfab.com/
- http://duolingo.com/
- http://simplymeasured.com/
- https://getsatisfaction.com
- http://www.jolicloud.com/
Not really SAAS but nice landing page :