The NGS Coordinate Conversion and Transformation tool, or NCAT not only provides technical assistance with the proper mathematics for making conversions and transformations, but it also provides information about a wealth of additional services that the NGS offers via the drop down menus on the website. If you are going to flag a NGS page this is the one.
The site supports lat/long/height, state plane coordinates, UTM, XYZ and more. You can also select the input and output datums. The site allows you to upload multiple points for batch processing and to download the software.
There are links to information about the NGS, data and imagery, surveys and more. This is a valuable resource.
For more information click here.