CBC collects books for a sale once a year, and probably some community groups as well. I know that Briar Hill school has a book sale every year.
Places like Goodwill and Salvation Army will take books, and I suspect Value Village as well. Homeless shelter is probably a good option, and maybe churches for rummage sales might accept them.
Here is a link for places in Calgary that accept book donations. Also suggestions like BookMooch and freecycle. I will also add Book Crossings - do a search for them, and leave the books around town.