Inkscape is pretty darn cool. I’ve only dabbled with it a little bit in the past, when I needed to generate some high-res OGRE logo images for our CafePress Store and :wumpus: handily converted my bitmap logo into SVG for the purpose. SVG stands for Scalable Vector Graphics - basically it’s an XML standard which defines how images can be built from lines, curves, fills, patterns and various operations on all of the above. Because it’s based on that technique rather than pixels, the images can be scaled to any resolution and still look good - think of it like windows clip art, but considerably more standard. It’s been around for a good few years, and because it’s XML, it’s easy to generate - for example at work we use SVG to automatically generate all our text-based web button images - you say ‘gimme a button that says Next’ and lo, you get a button image that says Next, in the right style and the right size to fit the text. And if you change your mind on the style of the buttons, they can be regenerated in bulk - nice.
Inkscape is a free and open source WYSIWYG editor for SVG, and it does a very good job of it too. I decided to play with it today because I needed to visualise something, and to do it on paper I really needed a couple of acetate overlays, which I didn’t have. So, I used Inkscape and its layers instead. The result isn’t artistic, but it helped me get my head round the part of Kadath I was working on, so everybody’s happy. I’m sure someone with artistic talent could come up with something really good with it, I found it very easy to pick up and use.
Related to Inkscape is the SVG-based Open Clip Art Library too - not only is it technically savvy, it’s artistically much better than most free clipart you’ll find on the web (which is mostly awful).