I'm not sure that there are many "great" courses without bunkers, but I will say that MANY of the first courses I played growing up didn't have bunkers. They simply couldn't afford to create and maintain them, as they tended to be rather utilitarian affairs of 9 or 18 holes, available to the public and without pretense of any kind.
The funny thing is that as I sit here thinking back on many of them, they did tend to use natural features in creative ways that would be appreciated by many on here. In fact, although the courses were assuredly not world class, they did include holes that played wonderfully, again and again, and I truly didn't know what I was missing.
Interestingly, many of them did include grass bunkers in place of sand. I tend to think they played more difficult, simply due to the inability to put spin on the ball from the rough.
All of that being said, I still love "great" bunkers, both from a visual as well as psychological perspective. Still, way too many of the bunkers built today have neither attribute, and are seemingly simply placed for color contrast.