I use Numismedia.com when I don't have access to a recent Greysheet. Their prices seem to be fairly up-to-date but you have to be a subscriber to access the listings for uncirculated and proof coins.
I have to disagree with you and agree with Bone. The Redbook doesn't pretend to be an accurate going price, but you can learn a lot by comparing what is in the book to dealer prices over a number of years. Eventually, you develop a feel for what things should cost. Sure, there are more current price lists, but price and value aren't always the same thing, and buying a coin for 10% off of the greysheet price can be enormously overvalued at times. Keep in mind this thread was originally about "coin values" and not coin prices.