One of the popular programs for PCB tracing and circuit diagram drawing is Eagle from Cadsoft. The software is available for Windows, Linux and Mac operating systems.
Freeware version of software has some limitations: The usable board area is limited to 100 x 80 mm (4 x 3.2 inches), only two signal layers can be used (Top and Bottom) and the schematic editor can only create one sheet.
But such limitations are not very bad for novice and amateur users. You can download the software from site at: http://www.cadsoft.de/ .
The component base are quite big. There is user exchange ftp in the site. And it is very easy to create new element by yourself.
The bad sides of the program: autoroute functions is very dumb. No autoplace function. And one problem with pads and holes. Some elements have very small pads and I can’t increase the size without editing library.