There is Terragen 2, much beloved and the favorite here. World Construction Set, not too easy to use from what I remember in the 90's when I had it. And the much reviled and maligned Vue. Vue has many issues, it can do very good stuff, but from my experience with Vue Infinite PLE, costs much too much.
Users of Terragen 2, and Terragen Classic, get the benefit of the developers actually reading the forum. They offer advise and help solve issues very quickly. Plus, everyone here tries to help each other. In other words, Great Programs and Forum.