Gimp is installed on stat network which can load, edit and export many graphic formats. It should be able to accomplish most of your graphics task.
xv is mostly a image viewer as its name X-viewer impiles. It can also be used as an image capturer, which becomes very handle if you need to write a tutorial with pictures of working applications.
Figure 1 of this guide is drawn in xfig. It looks like the paintbrush in windows but has more functions and uses vector format rather than bitmap. Its .fig file can be exported to a variaty of formats, including .eps, .jpg, .png. It is advised that you export your figure to both .eps and .png since latex uses eps inserts and pdflatex uses (by default) .png format.