Here's some information on how each of the currencies will be converted in the next content patch. Keep in mind these values may change, and they can get a bit math heavy. Just know that our intent is to appropriately value each mark and provide a conversion we feel is fair.

The following items are immediately converted to gold:

Emblem of Heroism = 5.5 gold each
Emblem of Valor = 5.5 gold each
Emblem of Conquest = 5.5 gold each
Badge of Justice = 1.833 gold each

Your New Honor Points total will be the sum of the following amounts:

Old Honor * 0.024
Old Arena Points * 0.85
Battleground Mark of Honor * 2.976
Wintergrasp Mark of Honor * 19.08
Stone Keeper Shard * 1.6
Venture Coin * 3
Spirit Shard * 1

Your Justice Points total will be equal to (Emblems of Triumph + Emblems of Frost ) * 2.75

Again, the softcap for both Honor and Justice conversions is 4000 points. This means that if a character converts to above 4,000 points, it will not be possible for them to earn more until they fall below the 4,000 cap.

A hardcap will be implemented in a following patch before Cataclysm's release. At that time, any excess points above 4,000 will be converted as follows:

Honor points above 4,000 are converted to gold at a rate of 35 silver per point of Honor.
Justice points above 4,000 are converted to gold at a rate of 2 gold per point of Justice.