The programs below are known as tracing tools of various types. I recommend if you are working a lot with scanned images, you might want all of them. They share common features in their ability to open bitmap files and convert them into vector format. This can very desirable if you have artwork, which needs to be replicated or reproduced with high fidelity. The reason I suggest all is they use different algorithms for performing conversions.
Autotrace / FrontLine - can use Imagemagick to convert to many different formats. Frontline is a GTK gui front end to access the many command line options.
Delineate - A java based front end to both Autotrace and Potrace. The neat thing is it converts directly into SVG.
Potrace - works in black and white, but does have a very good tracing routine. Potrace also has a GUI front end written for Qt 3.x
Pstoedit - is slightly different in that it specializes in the conversion of PostScript in to vector using Ghostscript. It works as a plug-in for GSview.
The thing to keep in mind when using these is there are many options when performing traces and some experimentation is sometimes required, especially more complex artwork. Don't expect perfection. The first time, it took me a bit of experimenting when I converted the Scribus logo from an EPS with a bitmap embedded into pure SVG, which then imported in Scribus.