http://www.tweakguides.com/ has lots of information to "help you understand and optimize your computer."
I would recommend the following sites for computer hardware reviews:
http://www.phoronix....n.php?page=home (Uses Linux, for those that like that.)
http://www.techpowerup.com/reviews/ (The best PSU reviews I've seen)
http://www.guru3d.com (Not for PSU reviews!)
http://www.vortez.net/ (As above)
http://www.eteknix.com/ (As above)
http://www.frostytech.com/ (CPU cooling)
The top two would be the main ones, with the rest not sorted in any particular manner.
A lot of these sites also have computer or technology related news.
http://openbenchmarking.org/ is a Linux benchmark site that has data from many users running the Phoronix Test Suite. It gives the data, including graphs, and various data sets can be compared (if you know how!).
For a comparison of the different PSU reviewers, check my Google Docs spreadsheet comparison table.
An excellent place for help with Windows is http://www.sevenforums.com/ https://www.eightforums.com/ or https://www.tenforums.com/
If you have any comments, please make them. I welcome any recommendations for sites to add, etc.
Updated 15/6/19: Removed a few sites, and updated / fixed a few links.
Edited by LinuxUser, 15 June 2019 - 10:33 AM.