My two main go-to programs for model railroad track design software are SCARM and Anyrail.
SCARM:
SCARM (Simple Computer Aided Railway Modeller) is such a powerful, and FREE, program. you can design a layout of near infinite complexity with it. Its amazing… And did I mention it’s for free! There is a bit of a learning curve to it, but once you get your head around it there will be no stopping you!
I’ve had dealings with the author Mixy on a forum I frequent, he has always been a great person to deal with, and keeps us in the loop whenever he’s updated anything. Top bloke.
You’ll also find some great tutorials and ideas on the SCARM website.
Find it at scarm.info
Anyrail:
Anyrail is a pretty powerful bit of kit too. And very user friendly. The free/demo version of Anyrail lets you play with 50 pieces of track on your virtual layout at any one time. Its pretty handy for generating layout ideas, throw a bunch of virtual pieces into a layout space and flip, swap, rotate them all about, see if anything inspires you. As far as I know, the full version of anyrail runs to about $60 US.
Find it at anyrail.com
Its worth noting that these programs are not scale specific. Their track libraries include many brands of set track in all of the major scales (O, HO, OO, N, Z G, etc)
Edit:
A new contender? : Trax
Recently I received an email from Fedor at TraxEditor.com about his new web-based program for model train layout design. It looks like a pretty neat idea!
I could have used a cloud based service during our primary design and construction phase. I was playing around with track layouts at night at my house, where the construction was at my dads house. It was a pain installing programs on his PC and transferring files back and forth between pc’s.
I’ll create an account and give it a try soon and let you know how it goes!
Cheers,
Adam