I was recently made aware of a free modelling tool called SolveSpace.
Autodesk Meshmixer is one of my favourite apps for 3D printing.
Autodesk have been making a big push into the 3D printing software space, mostly with free software like the fantastic Meshmixer.
A relatively recent newcomer to the CAD world, Onshape is riding the waves of Cloud computing and aims to set the standard of industrial and product design of the future.
To truly exploit 3D printing technology you need to be able to make your own models.