I'm going to list mine in the free section on craigslist and leave it on my porch for pickup.

I listed some things on craigslist, some (flooring/paint chips) on my neighborhood facebook page. I found that crafters and dollhouse makers like them. Carpet samples I dropped back to the store as convenient. Hardware -- I would try either of those or donate to Habitat for Humanity.

My various stone samples went onto my garden paths.

In my community we have several "buy nothing" type Facebook pages where we can give/"gift" things to other people. There are usually rules about meeting locally - in a local store parking lot, for instance - which makes it more convenient than meeting someone in another town. It's also safer than inviting a stranger to your home.

You could probably do that with most of your samples. The hardware could be used in crafts, for instance, or in a place where no one cares if the pieces match - maybe in a shop/shed cupboard. Stone samples - sure, in a garden path. And - people find amazing uses for the most unusual objects!

Freecycle

Many companies have to pay dearly for the samples the KD's use. For them wash to their hands of them and not make sure they're returned is ridiculous.

Would an art center have a use for them? I'd think some of them could be useful for collages/mixed media sculptures, etc.

Habitat for Humanity Restore donation

We lose samples all the time with people who've borrowed and never returned. Many times, tile samples are given pretty freely from the tile vendors, but samples of countertops and cabinets chips, those cost quite a bit of money. Those should be returned to the cabinet shop, if possible. I like how The Tile Shop does it. You pay for your sample. Per the SF... if your tile is a 12 x 12 and it's 3.50/sf, you pay 3.50. Bring it back in good condition, you get your money back. Smart. We are not set up that way, though. It isn't so bad for the customers who then buy with us and pay 20,000 for a remodel. But those who are just looking and take stuff with them to never return, that adds up.