A Gitzo Explorer or similar tripod works very well for low-to-the-ground macro photography. All three legs adjust to different angles independently, as does the center column. You can position the camera a few inches off the ground, and you don't need to worry about setting up on a flat surface. Gitzo makes a number of Explorer models, and there are some Asian knock-offs such as Benro that are less expensive and may work just as well.
You also should consider a ball head with versatile positioning. It's one thing to position the camera low to the ground, and another to do so with the camera at the proper angle, and to be able to adjust the camera angle without having to reposition the tripod legs and column. The Gitzo ball head mentioned in the previous link seems to have a lot of degrees of freedom. Other options would be a ball head with multiple drop notches, such as those made by Really Right Stuff.