IceSL is a modeler and slicer, all in the same software. Think of it as OpenSCAD meets Skeinforge.
By directly slicing the models IceSL avoids the expensive mesh CSG computation that most other softwares have to perform. In addition, IceSL relies on recent GPU algorithms to speed up visualization as well as the slicing process. On-screen preview is accurate and slicing is fast.
Beware that we have super-high GPU requirements, and that IceSL is highly experimental software.