What are some of your favorite FRs, guides, or any thread from seddit?

Due to the nature of reddit old posts simply disappear and are very difficult to read and find unless you were there. This thread is a revisiting of old yet very useful threads so newcomers to seddit will be able to benefit from. They can be guides, FRs, discussion topics or anything as long as the information is very valuable. The focus though is on FRs since most guides are already in the FAQ.

No joke posts please.