Pre-ordering Modern Warfare 3 gets you early access to the open beta, coming to PlayStation before other platforms, and access to the campaign a week earlier than everyone else. You'll also get some KontrolFreek thumbsticks if you order the game exclusively through Walmart.
Physical Editions of Call of Duty: Modern Warfare II can be pre-ordered for PlayStation and Xbox consoles. All Physical Editions on consoles include Early Access to the Call of Duty: Modern Warfare II Open Beta* when pre-ordered at participating retailers.