Inkscape (<a href="http://inkscape.org/" rel="nofollow">http://inkscape.org/</a>) is a very complete open source vector graphics editor (similar to Illustrator).<p>It has probably the best set of node editing tools of any vector editor I've used. I now use it exclusively for illustration, web design etc.
Creature House Expression (<a href="http://en.wikipedia.org/wiki/Creature_House_Expression" rel="nofollow">http://en.wikipedia.org/wiki/Creature_House_Expression</a>) was a serious competitor to Illustrator. It offered bitmap-style 'painterly' graphics in a vector environment, and an excellent UI.<p>Unfortunately, CH was acquired by Microsoft... MS is kind enough to provide the original (wonderful!) software for free; just follow the links in the article. Full (superb!) documentation included.<p>Creature House was also working on an animation version of Expression called LivingCels. Both Mac and Windows betas were released; the Mac version is rather unstable. It was touted by the media as a 'Flash killer', but LivingCels was far more: a truly revolutionary animation package with automatic 'in-betweening' backed by the full Expression engine. There's a website (livingcels.com) with tutorials and documentation, and some download links; currently offline, but should be up again in the near future... ;-)
Erm... not to be a dickhead or anything, but Adobe has some pretty sweet software. Although, I'm not all "I LOVE ADOBE" - because I believe they bought their best products from Macromedia.