Inkscape - An open source vector graphics editor. If your looking for an alternative to Adobe's Illustrator software concerning creating vector graphics, this would be a good one to consider. It's goal is to become a powerful graphic tool while being fully compliant with SVG, XML, and CSS. Inkscape is under active development and new features are being added regularly.
Showcase
Inkscapers are finding this tool useful for a wide variety of purposes, as you can see from these examples.Branding
Branding is where you use a variety of applications to create a whole package.
Icons
Icons are probably one of the most popular use cases when it comes to using Inkscape. Almost all complete icon sets on Linux desktop are created mainly using Inkscape.
Web Design
Website design examples from Jakub "Jimmac" Steiner et al.