Over the years, I have used numerous Computer Aided Design (CAD) software packages. I think it would be difficult to overestimate the degree to which CAD has improved the design process!
Here is a list of the applications that I learned well and used regularly (these may be one or two that I've forgotten):
In addition to those listed above, I have also worked with these programs:
Meshlab - This is a great piece of free software which I often use for viewing and calculating the properties of CAD models.
RasMol and Yasara - I used these and several other molecular modelling programs (mostly for research)
Materialise, Mimics - Generates CAD files from medical scan data. I'm sure this process is much less painful now than it was 15 years ago!
??? - There was some other program in the 90s where the company dissolved, and the software became free. I can't recall the name, but I used it and followed its development for quite a while.