EazyDraw For Mac OS X
Originally downloaded April 7, 2007. I'm not sure how I missed this one when I was looking for a tool to help me envision a home addition last fall... but it just didn't come up in any of the Google searches I did, or in searches on MacUpdate and VersionTracker. And yet two of the screenshots are specifically geared to this drawing application... EazyDraw apparently can be used both for interior design tasks as well as remodeling/architectural drawing tasks. In addition, it offers a host of paint tools, blends, and more. It appears to fully support vector drawing, while also enabling bitmap editing as well. (I think!) The licensing is unusual... for $20, you can try it for 9 months with no restrictions, and a full license is $95.
Version as tested: 2.3.
Update 8/20/12.
EazyDraw is a truly fantastic tool for vector drawing, while also allowing opening and manipulation of bitmap graphics. It has a large number of tools for creating and editing shapes and line drawings. It supports layers and can add effects such as drop shadows to any given segment. EazyDraw also has excellent text support, enabling normal text entry but also including powerful tools for transforming text — much better than those in Photoshop, for example. I found the interface a bit on the ugly side, but it was also intuitive and fairly easy to get started. Mastering the program would clearly take some time, however. The functions are fast and vast: Highly recommended if you're looking for a lower cost alternative to Adobe Illustrator (which is, by contrast, a daunting program to merely try out).