EDIT: We do indeed know them all. Most biases are simply a "region" bias, where a region is a defined area on the map that is dominated by the listed terrain type. To have a region bias simply means you will start near the terrain your bias desires. For example, on an Earth map with a cold Scandinavia, all of Europe could be considered one "Tundra" region, which would mean that Russia with its tundra bias, is equally likely to start in Spain as it is in Sweden. River and coast biases are self-explanatory, and a non-region bias merely means the civilization will spawn in any region other than the aforementioned.
America: Rivers? (Patch notes say this was removed, but it still shows up in the xml)
Arabia: Desert (not oil, but the desert tends to have plenty of it)
Aztec: Jungle
Denmark: Coast
Egypt: Not Jungle or Forest (IE, they'll start in any region that isn't jungle/forest)
England: Coast
Inca: Hills
India: Grass
Iroquois: Forest
Mongolia: Plains (where horses are most common)
Ottomans: Coast
Polynesia: Coast
Russia: Tundra
Siam: Not Jungle
Songhai: Not Tundra
Spain: Coast
Other civs: Do not have any bias. Getting iron with Rome comes down to luck, alas
America: Rivers? (Patch notes say this was removed, but it still shows up in the xml)
Arabia: Desert (not oil, but the desert tends to have plenty of it)
Aztec: Jungle
Denmark: Coast
Egypt: Not Jungle or Forest (IE, they'll start in any region that isn't jungle/forest)
England: Coast
Inca: Hills
India: Grass
Iroquois: Forest
Mongolia: Plains (where horses are most common)
Ottomans: Coast
Polynesia: Coast
Russia: Tundra
Siam: Not Jungle
Songhai: Not Tundra
Spain: Coast
Other civs: Do not have any bias. Getting iron with Rome comes down to luck, alas