You may have noticed in the schematics I post for various projects that I use KiCAD for all my designs. It's a free and open source package with no limitations on part count, pin count or board size. The software is cross platform, supporting Linux, Mac and Windows, and on Linux you'll probably find it in your distribution's repositories. Unlike the other big open source electronics design software gEDA it is fairly intuitive and not that different from other commerical packages I've used (OrCAD or Altium Designer). Unlike cost free versions of proprietary software like Eagle there are no reasonable limits on the board size, part count or pin count that you can create with this software and while it lacks some advanced features such as more complex curved pad shapes etc. it is very stable now and is well up to commercial work.
The biggest problems with all the free EDA software about at the moment is the library availability. The big name software such as Altium Designer benefit from manufacturer support where the chip and component manufacturers actually make librarys of parts. Farnell are now making Eagle footprints available from their website product pages which gives it probably the best library situation of the free software, but the limitations on the free version are absurd.
I've been making my own library up by adding to and updating the original libraries that were with KiCAD when I started using the software several years ago. I've managed to include a couple of new libraries that have been contributed into my set and I've decided to publish it as a git repository over on github.
I'd like to do something more with these libraries to make them more accessible. At current I simply replace the library, module and template directories in the install folder with my own. This makes sure that all my libraries are listed in the programs by default and has the schematic libraries in alphabetical order which makes browsing a lot easier. I think the library software needs some sort of upgrade to allow more granular imports of footprints and for a better user-space management, it's not good practice to be messing around with the packaged files as this means every upgrade could over-write them.
If you clone my repository and add parts I'd love to get a pull request to try and improve this repository further.
KiCAD libaries have changed a lot since I wrote this post, particularly footprint files. Best to ignore this information now. KiCAD is still awesome though!