Yep, Renderosity as Lyno suggest is likely to be be any Poser artist's number one source of premade content (clothes - and plenty of it rather sexy
, characters, poses, expressions, lights, scenes, items etc.).
Or well, perhaps the second source - you're gonna need the base characters from Daz3D to get anywhere (Victoria 3, or the new Victoria 4, if we're talking about female characters), and they've got a ton of great content in their store as well.
Renderosity is also a very large 3D community with a ton of galleries covering most 3D applications - and active forums as well.
If you plan on using Poser for 3D adult content, you probably also want to check out Renderotica -
http://www.renderotica.com/