Most thrift stores accept yarn, I've picked up lots of acrylics and cottons there and seen good wools too. You can also post in the Charity and Buy/Sell/Swap forums here.
Check your phone book for the local senior center and see if they'd like it. A lot of older people like to knit and crochet, but don't always have the money for yarn. In fact, right now would be a good time with the holidays coming!
If they don't, Craigslist, Freecycle, the local grocery store bulletin board or Ebay come to mind.
Och! it would do a seniors' home good to see a young good-looking chap like you at their door with yarn to spare. Cheer up the old folks, I say! (I have two parents living in such a home, and Dad still knits).
You could always mail it to ME!!!!!!! I teach a knitting class and we have been knitting shawls for residents at a local nursing home!! We can always use some new (to us) yarn, especially some that's machine washable/dryable!!!
Or if you'd rather look locally, check and see if your local library has a knitting or crocheting class. I'm sure they could use it.
If my husband would let me, I'd adopt all the unwanted yarn out there. I agree with a thrift store or senior center though. If I were still in Mississauga I'd help you destash it
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Jenny
alleusion on Ravelry
...I can't have too many projects, I still have empty needles...
I too, love to "adopt" unwanted yarn. You can teach kids to knit/crochet with it. You can make blankets (a.k.a. oddball pet snuggles) for animal shelters with it. Oh, the possibilities!