Scrap metal pile at the local recycling centre if it's stuff that's really knackered, like old chains/bent handlebars etc.
Some LBSs (DJ Cycles in Holcombe Brook used to be one – don't know if he still does) will take some scrap bits as they have their own scrap metal collected, but I'd expect that you'd have to a) be buying some stuff from them, and b) not take the piss.
As an aside, I manage to shatter a CF road bike frame (or rather the blue VW Polo that hit me did) & there are companies that will take CF for recycling too – Recycled Carbon Fibre in Dudley said they could recycle a CF frame, but I'd have to deliver to them.
Andy