I know for books there is addall.com, and for dvds dvdpricesearch.com
is great, but is there anything comparable for CDs? gemm.com doesn't
count.

There are a # of sites out there that offer mucis CD's at comparable
prices or let you choose from a list of new and used at varying prices
so that you can feel you have gotten the best price, or more
accuratly, what you wanted to pay.

I personally use overstock.com for many many items. They have very low
prices to a lot of the stores in my area
http://www.overstock.com/cgi-bin/d2.cgi?PAGE=STOREPICK&STO_ID=3&STL_ID=10

Also
http://www.amazon.com/exec/obidos/tg/browse/-/3023481/ref%3Dtab%5Fm%5Fgw%5Fl/002-5571530-7377611
which is a link for CDNow

And, as mentioned by a site member in the comments
http://www.pricegrabber.com/home_music.php/

You can also check www.amazon.com for music as well.

It's hard though to get a "priceline" or "expedia" though for music.
With the RIAA and the companies up in arms, the price of music is not
very negoitable right now. It seems to be more piracy or full price.
It's not a great market for what you're looking for. Good luck, and I
hope you find what you want to listen to for what you'd like to pay.

If this answer requires further explanation, please request
clarification before rating it,

and I'll be happy to look into this further.
Nenna-GA
Google Answers Researcher

Not sure on your country but
http://www.priceguideuk.com/music.asp
http://uk.pricerunner.com/QuickCategory.jsp?category=cd
are both UK-based...

or
http://www.pricegrabber.com/home_music.php/ut=81432936f3e08ef8
http://www.shopping.com/xMP-Music
are US-based and look reasonable

This is a good price-comparison site for CDs:

http://www.amusicarea.com/

A great site for comparing prices is MySimon. Here's their music section:

http://www.mysimon.com/2001-4182_8-0.html?tag=bc