If you go to webuy.com (CEX) they buy and sell most electrical items, they are in both the UK and US.
What you can do there is search for your item and then see how much they will give you for it, you will see three prices
We buy for....
We exchange for ...
We sell for...
The buy for value is the amount that they will pay in cash to take the item off your hands, so obviously if your selling anything on eBay you want at least that amount if not more because they are taking it off your hands where as with eBay your paying the advertising rates, auction fees, paypal fees, postage fees, etc.
The exchange for rate is the amount of money they will give you if you take the item into them and buy something else from their shop. This is probably about the amount of money you should be starting your eBay auction at. Most of the time this is a reasonable price and your undercutting what people could buy the item for from places like CEX.
The sell for value is the amount that they will sell the item to you for if you wanted to buy it from them. This is the maximum value of the product and you'll be very lucky if you get that value from eBay, unless you sell it to someone who is unaware of CEX. The reason for this is that CEX is a large business, they have shops up and down the UK and US (and other countries), they have a lot larger advertising budgets than one person on eBay, they offer guarantees on the products and safeguards to ensure the item hasn't been obtained illegally. Where as someone buying it from you on eBay - they're buying it from an individual, with a small advertising budget, if they're lucky you'll offer a return policy, but usually nothing like the 3 month warranty that CEX can offer, and apart from your eBay feedback he has no way of knowing how legit the item actually is.
So as a guide I'd tend to look at the exchange price CEX will offer to you for the item and start the auction at that and see where it goes. Sometimes you may get lucky and people will buy it for more than they can buy it from in CEX, this tends to happen a number of times with auctions as some people get carried away and will overbid on items, but don't expect to get much more than the CEX sale price, or if you can't be bothered with eBay you could always take your stuff down to the local CEX and just hand it over there and take what they offer you - this is the quick and easy method as you get instant cash and you don't have the hassle of setting up your auction on eBay, and paying all the listing fees and everything.
One other thing though with CEX the price shown on the net depends on the grade of the item - some items it does mention the graded price for example mobile phones come in grades A-C and not working, this depends on how you've treated the phone and what you have with it. A grade A phone is something that is like brand new, no scratches on screen, original charger, original box, original manual, etc, grade B is a little bit lower, might not have original charger, etc, and grade C would be a phone that has no box, none original charger, no manuals, a couple of scuffs on it, although I got to admit I bought a grade C HTC HD2 from them once and was amazed it was grade C as I would have said it was more grade B than C and none working prices are obviously none working phones. Also bear in mind that if any of your items are mobile phones, check the battery, there is a small sticker on the top of all mobile phone batteries and it changes colour in the event of getting wet (i.e. when you drop the phone in the toilet!), and this is how CEX tell if a phone has water damage, if it's got water damage they probably wont buy it, or maybe offer you the none working price for the phone, even if it appears to work perfectly. Also if your selling on eBay you could include this in the listing as proof that the phone is in good condition.
Of course CEX isn't always 100% accurate with their pricing, but it will give you a good guide, sometimes limited edition items can be worth a lot more than the CEX price, this mainly seems to happen with limited edition DVD's and things.