No sugar. It's important to start with good coffee (freshly ground beans of decent quality), then I will often add milk. While I do enjoy black coffee the milk makes it even better, and more importantly it helps temper the caffeine (especially if I'm drinking it on an empty stomach). I picked it up in Japan where "milk coffee" and "milk tea" are popular (although they often add sweeteners, but I find the milk is sweet enough).

Have you tried exploring the wonderful world of tea? There are SO many kinds and varieties, so maybe that's more your thing than coffee. My advice is to go to a local tea shop rather than buy from the grocery store; the quality difference is astounding, and don't be afraid of looseleaf tea. Same thing with tea as coffee, you can add milk for a richer, creamier taste; because there's so many varieties of tea out there milk won't taste good with many of them (clashing flavors, or the milk overpowers the subtle tea flavor), but I've also tried some where the milk made the flavor of the tea stronger somehow. Milk + Jasmine/English Breakfast are great starting points.

(Edit to add: poor-quality and oversteeped tea will taste bitter and you'll be tempted to add sugar; I used to be lazy and drink my tea out of the same mug I was steeping it in but I now am diligent about keeping steeping time to 3-4 minutes.)