The Civilization 5 Wiki states the following for Babylon
Free Great Scientist upon
invention of Writing. Double rate of
generating Great Scientists throughout
The Bowman replaces the Archer, it is stronger in melee (6 vs 4) and ranged (8 vs 6). The Walls of Babylon replace the walls, they are stronger (7.5 vs 5 defense) and they increase the bombardement damage of the city.
Seven Cities of Gold:
for discovering Natural Wonders (more
if first to discover). Natural Wonder
provide double Culture, Happiness and
The Tercio replaces the Musketman, it is stronger (18 vs 16), has a 100% bonus against mounted units, but is more expensive (140 vs 120). The Conquistador replaces the Knight, but it can found cities.
and for the Inca
Great Andean Road:
Hill terrain cost
ignored. Half improvement cost;
improvements on hills free.
The Slinger replaces the Archer, it is weaker in melee (2 vs 4) but it has a chance to withdraw before combat. The unique improvement is the Terrace Farm, which is a farm that can be built on hills and needs no fresh water.
I also found this official announcement for Spain and Inca from Greg 2K of 2k games which confirms the information from the Wiki.