Google's Sketchup is a 3D graphics application that's incredibly powerful, especially if you consider that it's absolutely free. The free version doesn't have a lot of the features of the full 'PRO' version but it has enough features to do most of what I've needed to do with it. In the 'Alternatives to MS Paint' page of this site, you were introduced to the program in a very general way. On this page, you'll see what it takes produce simple objects (which, when combined, can be used to produce more complex items).