There are three major players in the 3D market of human figure sculpting, posing, animation and rendering:

1. Poser by eFrontier (formerly CuriousLabs) was recently acquired by Smith Micro and enjoys huge worldwide recognition and retail distribution. It's the reference. The content side (Content Paradise) where you can find more models in addition to the ones included with Poser is very active and popular too, although there are also a large numbers of artists who get their models from other sources such as the Digital Art Zone, aka DAZ3D.com, where you'll find the very popular Victoria and Michael models.
   
2. Quidam  is perhaps the new kid on the block from N-sided, a French firm co-founded by former Amapi-expert Pierre Bretagnolle.  It is blessed with a great user interface and excellent tools and features for professionals who use high-end 3D tools for animation and rendering: they just want to save time creating, sculpting and painting & texturing their human figure models. The focus is on sculpting, modeling, texturing and posing, whereas the animation is left to the main 3D tools such as 3dsMax, Maya, Cinema, Carrara etc...
   
3. DAZ Studio (D|S) - discussed here. Developed over several years, it was one of DAZ's first major undertaking to diversify away from just being a supplier of content, and add applications to their product offering.They also now own Carrara and Bryce and they're making good progress with DAZ|Studio, continuosly adding new features, improving speed and allowing it to be used with other applications: BVH motion capture support for instance. The interactive manipulation has become faster and better. We love the interface choices to mimic Carrara or Hexagon and others, making it 'similar' to what you're already familiar with. It helps. And animation has become a reality.
   

D|S is a free tool, with optional modules offered for purchase, targetting the professionals. For the starving artist and hobbyist who can't afford the commercial alternatives, D|S is a God-send.