For every organization with IT Projects, a good source control system is essential. The actual product to be used depends highly on the team size and to some extent on the project type (Windows/Web/Mobile).
For teams working with Visual Studio, the source control was generally Microsoft Visual SourceSafe (VSS). There are many alternatives to VSS like CVS (from the Unix and Open Source world) and Sourcevault (based on SQL Server backend). But many teams, especially SME preferred it as it came along with Visual Studio and was tightly integrated with it. Though VSS fulfilled basic source control (check-in, check-out), the product was aging and was crying for an urgent update with the release of .NET.
Finally Microsoft seem to woken upto this fact and have launched a solid road-map to VSS in may here. The basic idea of MS plan is to have two products, one aimed at Small/Medium teams and other for enterprises. VSS 2005 (Sequel to existing VSS with HTTP/HTTPS, Unicode, XML and 4GB DB Size) is the SME product and Visual Studio Team Foundation will be the Enterprise product (with Sharepoint Support and other Enterprise SDLC support).