there is a strong market for vintage keys and effects units. Ebay is superb for disposing of anything that is no longer required, in fact two years running my annual holiday was virtually paid for by disposing of 'stuff' laying around.
The trick is don't start too high, don't use a reserve and don't use buy it now.
here is a brief description of my method of selling
1) If you are new to ebay, open an account (and also a paypal account) and buy some small things you need (guitar strings, music books, sd card for your camera etc). This will give you some 'feedback' which is vital as a seller if you want people to trust you. Ebay won't let you sell for a couple of weeks.
2) CLEAN the item thoroughly and take two or three GREAT photos (the sort of photo you would expect to see on a brochure). if its a keyboard; one overhead shot, one panel view (showing some keys) and if there is an LCD display a good photo of the screen. a rear view is also good (of the keyboard I mean). DONT USE FLASH as it makes the gear look scruffy, instead use natural light from a window. Use the best camera you can lay your hands on....DONT USE YOUR CAMERA PHONE!
3) Start the Auction low, be honest with the potential buyers and test everything you can. If anything has been serviced, is particuarly good (upgrades, clear screen etc) mention it in the auction and also list any faults. Start it at the ammount you would be willing to let someone walk away with it if they handed you x ammount of cash. Paypal should be preferred payment method as it is easier for people to pay: and because of this you will get more bids.
4) work out shipping costs first and also state collection is ok (but make sure they pay cash on collection). Don't pack anything until the auction is finished though - someone may ask you a question that requires turning on the unit.
Ebay does have its drawbacks, but as long as you play by the rules there should be no problems. For example, if someone makes you an offer midway through an auction...ignore it. If someone asks you to deliver to a different address to the one registered with ebay...refuse. Always be honest with buyers, both in the description and with any questions asked (they are going to find out at the end of the day anyway).