Some of the larger charity shops sell furniture, and will collect donations for free.
Then there are specialist charities who collect furniture for distribution or sale to those in straitened circumstances.
And there's also Freecycle, part of Yahoo Groups. They're locally organised, with the aim of preventing stuff going to landfill. You sign up to the group, and list whatever you want to dispose of.
http://www.freecycle.org/
If it's rubbish, local councils provide an uplift service, some for free, some with a nominal charge.