If you worked with scanned drawings and regularly need to turn them into vectored images, then you'll find RasterVect a Godsend.

It's pretty much essential for anyone that works with scanned drawings and can transform raster drawings into vector format. Drawings can be imported by vector formats in DXF, WMF, EMF, EPS and AI. Most CAD applications support this format such as AutoCAD, Corel Draw so you can go on to further edit them in those programs. Options include zooming, scrolling and color selection. RasterVect also features TWAIN support for importing from any scanners; the ability to automatically recognize orthogonal and inclined lines, as well as arcs and circles. You can also maintain the scale of the initial paper drawing and transform grey and colored images into black-and-white. For those that have to work with complex shapes and angles, there is also support for lines, arcs and circles alignment.

An easy to use vectorising program that simplifies the whole process and is enough to deal with even the most complex shapes.