May be useful to anyone selling a car... This gets you the Dealer trade-in prices, but not the "private seller" price.
There are other free valuation services, but they all seem to me to quote highly optimistic prices, and a dealer is likely to be using Glass's figures or something very similar.
Go to: http://www.vauxhall.co.uk
Select: Owners -> Value your car
"Glass's part exchange valuations will normally cost you £2.95 for 3 trade-in values and one retail from http://www.glass.co.uk
Vauxhall are paying Glass's for the 3 trade-in valuations on your behalf, to take advantage of this
free service click on 'Continue' below