NirSoft

NirSoft.net is the website of a sysadmin developer Nir Sofer who has developed a hundred popular, useful utilites for windows mostly for sysadmins, but some more general. Many still work in Windows XP (and Windows 95 and 2000, even).

I personally use these utilities almost every day.

Some examples:

• ProduKey v1.95
  ProduKey is a small utility that displays the ProductID and the CD-Key of MS-Office, Windows, and SQL Server installed on your computer. You can view this information for your current running operating system, or for another operating system/computer - by using command-line options.
• RegScanner v2.60
  RegScanner is a small utility that allows you to scan the Registry, find the desired Registry values that match to the specified search criteria, and display them in one list. After finding the Registry values, you can easily jump to the right value in RegEdit, simply by double-clicking the desired Registry item.
• MyEventViewer v2.25
  MyEventViewer is a simple alternative to the standard event viewer of Windows. As oppose to Windows event viewer, MyEventViewer allows you to search multiple event logs in one list, as well as the event description and data are displayed in the main window, instead of opening a new one. Also, with MyEventViewer you can easily select multiple event items and then save them to HTML/Text/XML file, or copy them to the clipboard (Ctrl+C) and then paste them into Excel.
  Supports Windows XP. For Windows Vista and beyond, use FullEventLogView
• BlueScreenView v1.55
  BlueScreenView scans all your minidump files created during 'blue screen of death' crashes, and displays the information about all crashes in one table. For each crash, BlueScreenView displays the minidump filename, the date/time of the crash, the basic crash information displayed in the blue screen (Bug Check Code and 4 parameters), and the details of the driver or module that possibly caused the crash (filename, product name, file description, and file version).
  For each crash displayed in the upper pane, you can view the details of the device drivers loaded during the crash in the lower pane. BlueScreenView also mark the drivers that their addresses found in the crash stack, so you can easily locate the suspected drivers that possibly caused the crash.