Desktop productivity tool No. 6: Inkscape 0.48
Free software's answer to Adobe Illustrator, Inkscape is polished, powerful, and loaded with tools that don't require a lot of guesswork to use well. Its native file format is conventional XML, and it can import and export from a whole bevy of existing vector and raster formats, as well as PDFs. The most recent version, 0.48, adds multipath editing, improved text handling, an interesting "spray" tool, and broad support for ICC color throughout the program.
Sophisticated tools and precise controls make Inkscape powerful enough for most vector art and design work.
Desktop productivity tool No. 7: Dia 0.97
A simple tool, but not a simplistic one, Dia is a flowchart and diagram drawing tool that is much like an AbiWord for illustration, in that it gives you only what you need to create a certain class of design and doesn't burden you beyond that. The controls can be a little persnickety; it assumes, for instance, that people will draw new shapes by starting at the top-left corner and moving down and to the right. (You get odd results if you try drawing objects from right to left.) But for the most part, Dia is easy to use, and it comes with a whole slew of common object categories -- electrical, hydraulic, programming, and so on -- that make it easy to jump-start a drawing of most any sort.
Creating a quick design with Dia. The elements in the Flowchart box at the left can be replaced with primitives for a great many other applications.