Lighter roasts, and maybe different origins, if you're making your own coffee. The Strength 3 Kenyan and Rwandan coffee in my local supermarket tastes a bit sweeter than the norm to me.
I've always taken coffee with a little bit of milk and no sugar. Not a latte, just a black coffee with a drop of milk at the end to take the edge off. It's not calorie-free, but over the course of a day it adds up to about a small cup of milk, which I can live with.
Have you tried cold-brewed coffee? Water can be added as needed to reduce bitterness without affecting the flavor too hard. But you may want to ask yourself if the problem is bitterness, or that you just don't actually like the flavor of coffee.
I've always taken coffee with a little bit of milk and no sugar. Not a latte, just a black coffee with a drop of milk at the end to take the edge off. It's not calorie-free, but over the course of a day it adds up to about a small cup of milk, which I can live with.