Enfamil
Visit their website and sign up for mailings and offers. They'll send formula samples and checks that can be used as coupons with brick and mortar retailers.
Check their e-store which sometimes sells formula at a discount with free shipping.
Call and request to be enrolled in their multiples program; they'll send you a free carton of whatever formula you're on. You'll also need to fax in copies of the twin's birth certificates. Call number is 1-800-222-9123. Alternatively, you can send a letter requesting to be enrolled in their Multiples Progam. Mailing address for the letter is Mead Johnson Nutritionals, 2400 West Lloyd Expy - B215, Evansville, IN 47721.
I sent my letter last month and just recently received twelve 12.5oz cans of formula in the mail. SWEET!
Similac
Visit their website and sign up for their StrongMoms' progarm. They will also mail formula checks regularly as well as educational brochures.
The website sometimes have printable coupons that can be used with retailers.
Purchase from their estore if the sale price is good
Call 1-800-222-9546 and register to receive free formula samples and checks
Gerber's Good Start
The website allows you to register to receive coupons in the mail. You can also call 1-800-443-7237 to register or send a letter to "Gerber Products Co. 445 State Street, Fremont, MI 49413". Copies of birth certificates will need to be mailed or faxed.
Earth's Best Organic
Visit the website for printable coupons.
Register to receive coupons by calling 1-800-434-4246 or writing a letter to "Consumer Relations, The Hain Celestial Group Inc, 4600 Sleepytime Dr, Boulder, CO 80301".
Are you a visiting parent? Did I miss anything? Please leave a comment to let me know.