Ideally these are tweetable quotes that act as social proof for your product from other users. These quotes could come from beta testers or early adopters. I find that most happy customers will oblige you with a great quote if you just ask.

For example: "Within 7 days our client had 1,500 signups to the service with $0 Adwords or ANY OTHER PPC spend and an very healthy conversion rate of around 35%" - Some Name Here If you really don't have customer quotes then you can grab quotes about your industry from trade magazines.

It will look like, to the visitor on your landing page, that these quotes are about your product... but really they are just quotes related to solutions like yours. For example: "Many start-ups were indeed able to launch to a strong following through collecting interested users, email addresses, Twitter followers well ahead of their public appearance using launch pages." - Smashing Magazine