cl.exe
which, while it's intended for use with the .NET framework,
is the same compiler that comes with Visual C++ Standard.
Since this is the .NET SDK, it doesn't come with the headers and libraries required for Win32 API development, as these are part of the Platform SDK. Lo and behold, the Platform SDK is free as well. You only need the Core SDK, but feel free to download the other components as you desire.
As a bonus, if you download the Platform SDK documentation (which I highly recommend) you will have a complete local and up to date Win32 reference which is MUCH easier to use than MSDN online.
Remember to check the options to Register Environment Variables in both SDKs, otherwise you'll need to set up the PATH and other variables yourself before the tools will work from the command line.
To build a simple console application:
cl foo.c
To build a simple windows application such as the examples on this tutorial:
rc dlg_one.rc cl dlg_one.c dlg_one.res user32.lib