AuthorIT - Tour of main features, free trial version of this tool. Also detailed product information, examples, support pages, user forum. - http://www.authorit.com/
Helpmatic Pro - WinHelp and HTML help authoring tool for creating professional help files quickly. FAQs, reviews, download trial, ordering information, and upgrades. - http://www.helpmatic.net/
HyperText Studio - A visual HyperText authoring package which makes it easy to create and manage Windows Help files, Web sites and HTML Help files. - http://www.olsonsoft.com/
HelpHikes Pro - Create detailed, non-trivial help files for Windows. Drag and drop links between your topics and test them at design time. Manage big help projects easily with the unique hypertext folder-based approach. - http://kanadepro.com/helphikes/
Sevensteps - Development tool delivers plain HTML and WinHelp from one XML source. Free trial version available. - http://www.sevensteps.com/
Software Interphase - Authoring system including ForeHelp, Help Magician Pro, and WinHelp Sorcerer. - http://www.sinterphase.com/
Help to RTF - Help to RTF's converts Windows helpfiles into RTF-formatted document files compatible with Word. The converted RTF documents include the associated BMP, WMF, SHG and HPJ files. - http://www.herdsoft.com/catalog/ehlp2rtf.html
HelpBreeze - A WinHelp, HTMLHelp and HTML help authoring program. - http://www.solutionsoft.com/hlpbrz.htm
Instant Help Pro - A generator and editor for WinHelp and HTML Help. It automatically creates the help system and updates the source files and project files of a Visual C++ Project. - http://www.georgscheidel.de/html/inshelp1.htm
EasyHelp - A development tool that creates help files from Microsoft Word documents. FAQ, mailing list, free trial download. - http://www.easyhelp.com/