I plan to buy a new car soon and would like to have a clear idea of
just how much is a reasonable price. It is ten years since I last
bought a car, and at that time I used a site that showed exactly what
the true dealer cost was for every item, as well as showing holdbacks,
incentives etc. I cannot locate such a site: there are many that show
the invoice price, but none like the one I used before. Most seem to
be a front for dealers, since you have to submit your email address
and have a dealer send you a price. This is not what I am looking for,
at this point I do not want to have any dealers involved. Does anyone
know of a site similar to the one I have described?

Go viosit the library and look in Consumer Reports. You could visit
their website and pay a small fee, but supporting your local library
is important.

I would use several online tools to understand the price for your car:
kbb.com, edmunds.com, carpoint.msn.com.  Using these sites will give
you a good idea of the options and prices. Then visit at least 3 local
dealers and negotiate their best price using the "invoice price" as
the start for the negotiations, not the sticker price. Then submit
your information on a couple of the websites that get you quotes from
dealers.  Using the 4-6 quotes you now have should give you a good
idea of the fair market price and which dealer will accept the lowest
price. Go to the best dealer for a final negotiation. This strategy
helped me get very good prices on my car purchases.

I recommend using Consumer Reports, as mentioned above by markvmd.
Their car price service is not free, but it can save you a heck of a
lot of money.

http://www.consumerreports.org/main/newaps/aps_home.jsp?aps_type=new&KEYID=nc5&KEYADID=nchome