While Autodesk is still talking about adding 3D to its AutoCAD WS software, IMSI/Design has delivered its second release of TurboViewer Pro, which displays 2D and 3D CAD drawings. The non-Pro version is free; release 2.0 of the Pro edition is $20.
The primary feature in this new release is the support for 21 file formats, including multi-page formats (see list after the photo).
The viewer supports model and paper space layouts, SHX and TrueType fonts, and custom perspective 3D viewpoints.
TCW - TurboCAD for Windows
2CD - DoubleCAD
DCD - DesignCAD
3DM - Rhino
DGN - Microstation (2D only)
DWF - Design Web Format
DWG - AutoCAD Native Format
DXF - Drawing eXchange Format
FCW - FastCAD Windows
SKP - SketchUp
ASAT and SAT - ACIS
IGS - IGES Drawing
OBJ - OBJ Drawing
STEP and STP - STEP
3DS - 3D Studio
CGM - Computer Graphics Metafile
EPS - Encapsulated Postscript Format
PDF – Adobe Portable Document Format
PLT - Hewlett-Packard HPGL plot files
STL - Stereolithography
WRZ - VRML Worlds
The only way to get it, unfortunately, is through Apple's online software store. We await the Android version.
[Disclosure: IMSI/Design provided the iPad with which to test the software, which I can't, because Apple locks its app stores to countries.]