MaximumPC posted 21 Essential Steps to Make Your PC Better/Stronger/Faster, and it seems really good. It doesn’t have the “Run this random registry optimizer program and delete all your Prefetch files” type of pseudo-advice that other sites give. Some is of no use to the normal user (please don’t overclock anything unless you already know what it is!), but a lot of it is stuff anyone can do to help keep things in good shape.
Another link: PhotoRec. A friend of a friend deleted a bunch of photos from her camera. I’ve used PhotoRec a few times, and it’s amazing at retreiving deleted files, but the terminal interface isn’t at all beginner-friendly. I may try posting a quick tutorial on how to use it at some point.