Freeware Regmon is a Registry spying utility that watches and displays information on system-wide registry accesses as they are occurring. This makes it a uniquely powerful tool for learning how Windows works or tracking down problems due to misconfigured Registry settings. Version 4.0 unifies previous NT and Win9x-specific versions of Regmon into a common interface. Full Source is included. This sites been around a long time, and they do a great job.
Software is rated, and easy to find, but some days the site seems a little slow.
Literally hundreds of programs are available. You get mainframe quality tech support, and the best tools all from one source. Well organized, and fast. However, you may have to wade through a ton of end user software before you get to applications that you may actually find useful. NT Shareware One of our favorite sites.