I have no experience with formula, but why won't anyone take it? You can't resell it, of course (though plenty of people do....), but I don't see why you can't donate unopened formula samples. I have three children and have had samples of Enfamil, Similac, and Nestle Good Start sent to me, and I've donated all of it. Many of the donations occurred after hurricanes (Rita and Ike), but I also donate it to the church.
***After reading the other responses, I really have to say you are NOT supposed to resell FREE samples. It's not allowed, and it's not ethical to sell something that was sent to you for free. Just my two cents, but churches will take it, you might have friends that will need it, a WIC person has said you can donate it to WIC, and Freecycle and Craigslist are excellent ideas. Please don't sell it - that's really not ethical.