In addition to delaying the cotton gin, you always have the old standby that negotiations over the Constitution go a little differently, or westward expansion gets fleshed out differently. A few states, like Virginia, has early support for compensated emancipation, including George Washington and Thomas Jefferson. A few butterflies flap their wings, and Kentucky and Tennessee could have been free states, while Virginia has a plan in place to end slavery within a generation.
The earlier you end slavery, the less racism there would likely be as well - most of what we understand as racism was cooked up over decades to justify the continued existence of slavery. It's hard to justify owning another human being, especially in a country where human beings are supposed to have rights - this is why later slaveowners increasingly viewed slaves as property, not people, and jumped through a number of insane hoops - head bumps, to name one - in order to justify that view, that the black man not only is not equal to the white man, but less then a man.
Most of the founders did not view blacks as inherently inferior - were you to say, introduce them to President Obama, they wouldn't be too shocked, because for many of them, class and education determined your status, not your skin color, and Obama is a well-dressed educated rich guy. You get a large population of free blacks early on, give them a generation to homestead, start businesses and educate their kids, and most importantly, plant the idea that given the same opportunity as white people, black people can succeed just as capably, and you strangle a lot of the roots of racism in the cradle, which strikes another blow against remaining slave states. It's hard for a South Carolinian slave owner to say slavery is the natural state of existence for the black man, when an abolitionist can point out to a host of black men up north that own land, operate businesses and serve as judges, sheriffs and even mayors.