These are always great to have on hand!! I love the samples to keep in my diaper bag (although my daughter is 16 months old so I no longer use these samples, but they are also great to donate!)
Parent's Choice Formula Sample
Enfamil Gentlease Lipil
Members Mark Formula (your choice or two)
Similac Advance Early Shield
Nestle Goodstart Formula
I registered for a few of these companies and most of them send you high value coupons and continued sending cans of powder formula for months after my daughter was born!