I would also recommend Simlab. It is easy and straight forward to use with a Windows standard type interface. The STEP AP214 format works great to render faces, and the 3DPDF output from Alibre works fine if you only need to render entire parts with a texture. The 3D PDF retains the tree structure of the Alibre model better than the STEP 214, but you can rebuild the structure inside of Simlab. Look over the Simlab thread for tips on how to use Simlab.
I have been looking at rendering software for Alibre for many years and not found many acceptable alternatives. Some people are happy with Maxell Render, and some have even had good luck with the free Blender render package. However, most rendering packages are very different from your standard windows interface and require a bit of a learning curve to get up to speed.
Another alternative is Adobe Acrobat Extended with the 3D toolkit for about $699 retail. It uses the same material application method to parts (not faces). I found it harder to learn, but there are some free videos on the net which now makes that easier. You can create textured 3D PDF files, and do renderings as well. Hopefully Acrobat 10 will contain the ability to texture faces as well (same as the Deep Exploration 6.1 product which has been re-branded as the 3D Toolkit), but it is still in beta testing. Unfortunately, the download demo from Adobe does not include the 3D Toolkit capability so there is no way to test if this option will work to your satisfaction. You can download the Deep Exploration 6.1 30 day demo, but that product is now even more ridiculously priced.
I also own NuGraf for rendering, but there is currently a problem getting files to that software now that the SketchUp exporter is no longer supported. The STEP translator package does not work very well with the Alibre exported STEP formats.
The biggest problem with any rendering software is to get the Alibre model into the rendering package, as renderers tend to use surface models rather than solids. Retaining the tree structure is even more difficult with the formats commonly used by renderers.
My favorites are Adobe Acrobat 3D toolkit, and Simlab.