SpudFiles

I like the free version of Alibre http://www.alibre.com/
It is an actual 3d CAD program (more focused on dimensions), not just a 3d modeling program.

It is very much like Solidworks, a popular and powerful 3D CAD program. If you plan on going into engineering then you probably have a pretty good chance of having to use Solidworks or a similar 3d CAD tool, so learning one now would help you out.

try using google sketchup,its free and i think its pretty easy to learn. Plus if any1 has any pre-made spudding models(pipe, valves, connectors, etc...) that would also be very helpful.