Txsparky has provided a good link. What you might like to know is that they offer a "free" limited feature program. Westinghouse/Cutler Hammer had a nice package, first for pay then distributed for free called Pow-R-Designer. This program superceeded it.
http://www.cutler-hammer.com/unsecure/html/prodesign/prodesign.html is the link to the sign-up form.
For ladder diagrams, I use the Constructor by CMH Software. Moving up from there, i use Visio Pro, and AutoCad [full current package]. There are a number of approved 3rd party developers that may have add-ons that could serve your needs. Both Pow-R-Designer and Visio export in .dxf format which is the AutoCad file format so that compatability is reasonably good.
