tips.txt comes with Windows 95. It provides various Windows Explorer command line options and several relevant keyboard short cuts. (Windows-E starts Explorer, i.e. hold down the Windows key and press E) You should also be familiar with the additional txt files in your Windows directory.
Computer Tips provides help on many topics, including Windows 95 Explorer and Windows NT 4.0 Tips
Windows 95 (tm) FAQ Provides general help
Windows 95 Annoyances is a good source of information. Also available as a book.
Freeware related to Windows Explorer and desktop functions. Many of these require the VisualBasic 5 runtime. Many of these are for Windows 95 only.
PC Magazine (ZifDavis) provides a number of utilities and hints.
Ron Badour provides a number of tips on configuring Windows and the registry.
This provides a description of the Windows Explorer Command-Line Switches.
Systems Internals provides utilities (and source code :) that allows you to monitor what is happening. In many cases, both Windows 95 and Windows NT versions are provided.
The Windows Registry Guide contains lots of searchable information on the registry. However, be warned that there are at least 2 flashing advertisements per page and that most pages are too wide to view on a 640x480 monitor.
A few Registry Hacks are available here. Included is a way to stop the icons from changing as you use the system (ShellIconCache gets full and a registry hack changes the maximum size). There is also a very good links page.
A large part of Windows Explorer appears to be implemeted vis shell32.dll. This can be verified using DLL Dependency Walker and Resource Hacker.
Microsoft provides information on how to customize Windows Explorer (the shell) including how to customize the context sensitive menus. In general, there is more data than I've presented in this document. However, some of it is presented in a manner that I find very difficult to follow. In addition, some of it is misleading or simply incorrect. (Specifically, see bullet 3 below.) Shell Basics/Context Menus explains that
|TweakUI 1.1||- Allows undocumented customization of the User Interface|
|CAB Viewer||- Allows browsing of the compressed CAB files|
Agent Ransack (free) is a super program which replaces the Windows Explorer search function - just right click any folder. In addition, when searching for a string, it actually displays the text lines that contain the string. Even more important, it searches ALL files (unlike Windows XP which searches only those files that Microsoft thinks that you should be searching.