My CAD experience had humble beginnings with TinkerCAD, as suggested by my high school librarians as a good beginner's tool for 3D modelling. I then found a slightly more advanced tool, Autodesk 123Design, which I used for a water bottle rocket project in High School physics class. For a longer period of time I used the educational version of Autodesk Inventor 2014, where I made some actually useful models such as weed whacker nylon spool caps to replace the broken one in my family's electric weed whacker. I also created small plastic brackets to hold the glass tabletop of my table on. I then transitioned to Onshape, a cloud-based CAD tool that works on any computer with an internet browser (no installations required). I really liked being able to hop on any computer (like at school) and pick up where I left off. I currently use Autodesk Fusion 360 for my personal projects.
Listed are the links for the parts I mentioned above, which were designed in various software:
More Onshape links to previous projects listed below are a design for a new window crank for my friend's truck. My largest project is my own design for a whole 3D printer built out of V-slot aluminum extrusions. More information about that can be found here.