Here are tools I've seen other people use:
- Blender
- SourceFilmMaker
- Garry's Mod
- Poser
- Second Life
- Custom Maid 3D 2
- 3D custom girl
- DAZ Studio
- Honey Select
- PlayHome
- MikuMikuDance (MMD)

Did I miss any? Blender is high-tier but could be useful for making small objects that you import into other programs. There are of course also other similar programs like Blender (like Maya for example) and I guess you could also use Unreal Engine or Unity to make 3D porn.

I've come to the conclusion that DAZ Studio is a pretty good beginner program, although I haven't tried it myself yet. Am I wrong? It's free and it seems to be easy to pose characters.