Several years ago I was given multiple bags (unopened, same dye lot per bag) of wool blend sock yarn. The local agencies I knit for do not want any wool clothing and the one I mail to only wants heavy weight wool socks. I have at least enough Kroy sock yarn to make 25 pairs of socks and am looking for somewhere to donate wool blend socks knitted with standard "sock" yarn (ie. 28sts = 4in on #3 needles).
So, you know my first response is ... make that yarn into Sockhead Hats and Basic Beanies! Both patterns use just about any "standard" sock yarn you have in your stash, and work up super warm while also being thin enough that you can send bunches of them for donation to a wide variety of charities.
But the real question was where to send those finished items, specifically who accepts socks. There's a few charities I know of that love to get wool socks all year long!
Nest: Maine, which has been accepting items for northern Maine residents for about a decade now, is always my go-to when people ask where they can donate woolen items. Nest accepts all manner of items, from hats and mittens to vests, sweaters, and even socks! All sizes are needed, and it's helpful to label the socks for size before you send them on over.
Another great organization is Hats And More For War-Torn Syria, which is actually a Ravelry group. What began as a way to collect just hats for refugees has become a global effort to clothe those fleeing war and disaster with wooly warmth. Socks are ALWAYS needed for this organization as well, and they simply request you tie the socks together with a spare bit of yarn so the pair doesn't get separated in transit. The Ravelry group has addresses both for the US and for the UK, so folks from all over the globe can ship to the cheapest option for them. All items are sent to refugee camp with aide workers through Salaam Cultural Museum, an internationally recognized aide group.
I hope that helps you out! And I'd love to see pictures of the items you make to donate - just tag them #shemakeshats on social media and I'll hopefully see them!!
(photo from the Kroy yarn page on Ravelry)