Software
CAD - I use AutoCAD for work and am therefore able to produce drawings easily, but it is prohibitively expensive for home-users. However, I have recently investigated DraftSight - a free, 2D drawing package that is surprisingly similar to AutoCAD, and well worth investigating.
Trackwork planning - For narrow gauge layouts with bespoke trackwork, I have developed some standard track components for use in my CAD programs, but for layouts using commercial trackwork, I use Anyrail, a dedicated model railway drawing package.
Trackwork planning - For narrow gauge layouts with bespoke trackwork, I have developed some standard track components for use in my CAD programs, but for layouts using commercial trackwork, I use Anyrail, a dedicated model railway drawing package.