In addition to American History told by Contemporaries, the four-volume set of US History primary sources printed at the beginning of the 20th century, I'm going to check every once in a while for other sources that perhaps shed some additional light on what people were thinking about these events in the past. There are fewer compilations of such accounts, especially of voices critical of the mainstream or the ruling party then or the dominant narrative more recently. One of these sources, of course, is Howard Zinn and the people who have followed in his footsteps.
A People's History is a valuable counterargument, and many of the sources it mentions are worth looking into -- if only to see if I agree with the way Zinn has used them. One such source is Bartolomé de Las Casas (1484-1566), a land-owner who emigrated with his father to Hispaniola in 1502 (at 18) and helped "pacify" the island. In 1506 he returned to Europe and was ordained. In 1511-13 he participated in the conquest of Cuba. Las Casas received an encomienda for his service, which in practical terms meant he was both a landowner and an owner of semi-enslaved natives whom he was nominally responsible for Christianizing.
Over time, as Las Casas observed the conduct of his fellow Spaniards and the devastation of the native population, he became convinced that the colony was unjust. He renounced his encomienda and became an advocate for natives and a recorder of the conditions and cruelty they faced. One thing to note: like all Europeans at the time, Las Casas had no idea of the way European diseases had affected native populations. What we now called the Columbian Exchange killed about 90% of native peoples throughout the Americas. Not understanding this, Las Casas attributed the depopulation of the Caribbean to Spanish cruelty and native suicide. Although this isn't the whole story, I don't think it detracts from his accounts of Spanish actions.