I have been reading a ton of message boards about pregnancy, especially about multiple pregnancies, and I found this awesome link with a long list of companies that offer freebies, samples, and coupons for families with multiples.
Some offer it for just regular pregnancies, but most are for multiples. Some you can just call and sign up for the multiples program, but most require you to send in proof (I am assuming birth certificates). Don't send anything with your child's (children's) social security number. Just black out things you don't want them to know.
I went through the list of phone numbers very quickly today and have a ton of stuff and coupons coming my way. When the babies are born, I am going to be sending their birth certificates to all the companies to get as much free stuff and coupons as I can.
I also went on all of the formula and diaper websites and signed up for their programs. Make sure you fill out both kids if you are having multiples or select the box for multiples as I think you get double the stuff and coupons.
Hope this helps!