Most of the major GIS software vendors now have a free introductory “viewer” available for download. These normally contain standard navigation and selection tools, and allow you to view datasets but not change them.
They are very useful if a company is about to invest in a GIS and are unsure what software to use. Point their employees to the following links, create a few datasets relevant to their organisation, and let them get a feel for each and find out their preferences. Clearly it will be the management who will make the investment so there will be a trade-off between cost and how much their employees like a particular product.
Of course you could always just recommend whichever one you feel most comfortable developing in..
“GeoMedia Viewer is an easy to use, FREE GIS software application for desktop viewing and distribution of geospatial data”
“ArcExplorer is a freely available lightweight GIS data viewer that lets you perform a variety of basic GIS functions. With ArcExplorer, you can display, query, and retrieve data. It can be used as a stand-alone application with local data sets or as a client for Internet data and map servers.”
“Map Reader provides users of Cadcorp SIS with a powerful free tool to effortlessly view, query and print map data. The strength of Map Reader lies in its ability to view over 160 formats..” (requires registration)