Unless they're very rare or sought after, you're not likely to get much for them.
My bloke's discovered a site called freecycle - www.freecycle.org - where you can advertise stuff free to good homes. You can get decent stuff that way too. We've just got a colour telly and a box of black and decker tools, and we've found good homes for a couple of speakers and a load of spare motorbike parts.
You don't get any money for anything, but at least your stuff is appeciated.