EazyDraw dubs itself as a "balanced vector drawing application," and from browsing its feature list, that sounds just about right. It looks like it has a nice array of illustration tools and abilities including some CAD-related features like wall and window tools, as well as drawing on a grid. EazyDraw can even import and edit old school files from Claris Draw, Mac Draw II and Mac Draw Pro.
EazyDraw is a Universal Binary, and a demo is available. Licensing the app, however, is a little strange: a full download license can be had for $95 (CD in the mail is $115), but you can also purchase a nine month license for a mere $20. Take that as you will, but if you've been looking for a solid and feature-rich illustration app, EazyDraw probably has you covered.