Core GIS Vendors/Platforms
The GIS marketplace has four key vendors that deliver "generic" platforms: ESRI, Intergraph, MapInfo and Autodesk. (Autodesk and Intergraph also produce other types of software while ESRI and MapInfo deal in GIS exclusively.) ESRI's ArcGIS is a family of products for the desktop (ArcView, ArcEditor and ArcInfo), but the company also offers solutions for developers (MapObjects), the enterprise (ArcSDE) and the Internet (ArcIMS). ESRI and its partners offer extensions to customize its products for specific industries. Intergraph's core platform is GeoMedia (with comes in a core and Professional version) and it provides extensions to it for various disciplines. There's also GeoMedia Web Map for the Internet. MapInfo's core product is MapInfo Professional for the desktop, but the company also offers developer components (MapX) and Internet solutions (MapXtreme). Autodesk Infrastructure Solutions Divisions develops desktop products Autodesk Map (built on AutoCAD), Envision (a desktop/Tablet product) and MapGuide (an Internet solution). All four companies have dabbled in location-based services to some extent.
The other two major players that weave into the marketplace are Oracle and Microsoft. Oracle Locator and Oracle Spatial are parts of the database that provide support for GIS data and funtionality. Microsoft's desktop MapPoint is a mapping program, but its online service, MapPoint .Net is gaining ground in that arena as it matures.
There are many other vendors that focus on specific disciplines (GE Smallworld focusses on electric, gas and telecom, for example), low cost solutions (Caliper, Manifold), imagery (IDRISI, PCI Geomatics, Leica Geosystems) and others. Another layer of providers produce add-on functionality for many of these platforms in the form of shrink-wrapped products and less formal services.
Everyone wants things for free. Many vendors offer free GIS viewers with limited functionality. There are listings here. There's a website for free GIS, and open source solutions.