If you're familiar with Inkscape, there are some trace utilities from their wiki under vectorize/trace section.
Potrace is now embedded into Inkscape. You don't need to run it separately.
Autotrace and Frontline (alternatives to Potrace)
Autotrace an open source vectorization program by Martin Weber. That means you can convert bitmap images (like scans) to vector graphics. While not optimal for photos, it does good job on line art and poster-like images. Doesn't do too well with color.
Autotrace has some features not available in the embedded Potrace dialog in Inkscape. For example, there is a centerline switch that is especially usefull for tracing roads (in maps) or font characters.
Frontline is GUI frontend to Autotrace by Masatake Yamato. Frontline can be run as standalone aplication, but it can also be directly accessed from Inkscape and GIMP.
If you want to have tracing option, you have to install both Autotrace and Frontline before compiling Inkscape. Inkscape automatically detects these programs, and adds inline raster to vector conversion option to image menu.
Both Autotrace and Frontline can be downloaded from Sourceforge. Binaries are available for windows and linux.
Front end written in java that does interesting things with color images.