What is the value of a 1879 gold Liberty head 10.00 coin?

Look on the back under the eagle. If there is a small S there, or no letter, it's one of the more common varieties worth anywhere from $510 to $620 as of 12/2008.

If there's an O (for the New Orleans Mint) it's more valuable - at least $2500 in moderately worn condition, 10 times that much if it's almost uncirculated.

If you're lucky enough to have a coin with a CC mint mark, you'll need to have it authenticated by a certified appraiser or dealer, because a Carson City $10 coin with that date retails for $10,000 to $45,000