In this time of the internet, its never been as easy to get some decent benchmarks of your cars value. Obviously we offer a car valuation service as do Car Max. If you are looking to sell your car I would recommend getting a range of online quotes from the above. This should give you a base price that providing you enter your details accurately, you should feel confident that you can get this price with relatively little hassle.
Online advertisers such as Autotrader can also give a good guide as to approximate pricing for your car, especially if you have a popular make or model. However, comparing cars with different mileages, years, specifications, or editions can be difficult. However, it still gives you a good feel for the approximate price.
Some people feel that their car would be more valuable to a specialist or collector. In my experience, most cars are generally far less "collectible" than owners like to believe. Whilst some cars are highly collectible, be really honest with yourself as to whether your car is truly a "collectible". I once worked for a major car insurer and it was amazing how many people tried to get specialist collectors insurance on fairly standard cars. Even if your car would appeal to a specialist, how easy will it be for you to locate them? One of the most expensive elements for car dealers with trade-ins is redistributing the trade-in to someone who truly wants it. Not all car dealers really want your car but they often have to offer a part exchange in order to sell you a new car.
Also be clear as to how quickly you need to sell the car. It never harms to put your car on the market before you actually need to sell it. Clearly if you get a flood of calls, it may be best to reconsider your pricing. Likewise, if its for sale for a long time, either your marketing is ineffective or your price is too high.
Many people I know sell their car quickly by parking on a busy road near their house with a clear price in the windshield and a contact cell.
If you decide to part exchange your car at a dealer, you are likely to command a fairly high price, but be careful - the dealer is subsidising the offer by making a significant profit on the car they are selling you. Don't get me wrong, you can probably get a decent deal if you negotiate effectively, but just be clear on why a trade-in price is often far higher than an outright offer just to buy your car.