Depends on what you want to do with it. There are many good ones. If you want someof the functionality that Dimensions gave you, you can find it in Illustrator CS2.
If you are looking to create photo-realistinc renderings or animations, then something a bit more robust is needed. Maya, Lightwave, 3D Studio Max, etc...
Many 3D proffesionals will have many tools they use.
Most 3d is designed for raster output. If your goal is Vector output then you may need a plug in to go with your raster 3d modeler/renderer.