Audacity is a free Digital Audio Workstation (DAW) that I use to record and edit my audio in. If don't have it already installed, I highly recommend doing so: https://www.audacityteam.org/download/
FFmpeg allows you to import and export m4a, mp4, WMA, and many many more audio files. If you use a phone this allows you to import your recording directly into Audacity and bypasses having to use an online mp3 convertor. (Word of warning: The website to download the plugin runs a lot of sketchy ads. The ONLY way to download the plugin is to click the proper hyperlink.): https://support.audacityteam.org/basics/installing-ffmpeg
Paul L's De-clicker and De-esser are must haves for editing. A de-clicker removes unwanted mouth noises and clicks. A de-esser is used to decrease the harshness of sibilance (S sounds): https://forum.audacityteam.org/t/updated-de-clicker-and-new-de-esser-for-speech/34283
TDR Nova is a real time 4 band dynamic equalizer: https://www.tokyodawn.net/tdr-nova/free/
TDR Prism is a real time spectrum visualizer which can compare the frequencies of multiple tracks: https://www.tokyodawn.net/tdr-prism/free/
Some simple effects that I don't really use except for the rotary and chorus when I want a unique distorted sound. It is nice to play around with real time effects though: https://www.musehub.com/plugin/musefx
Shape It is a really good real time 10 band equalizer that is professional quality with a lot of really useful tools. If you plan on eqing your audio, I highly, highly, recommend using this equalizer: https://www.musehub.com/plugin/shape-it
These plug-ins are not effects, but rather analyze your audio and see if they match the standards for multiple industries. It measures the peaks, noise floor, and RMS (basically the average loudness of your audio): https://github.com/AB9IL/audacity-plugins
Volume Stats is a really good analyzer for your audio which I use to get more detailed RMS data from my audio: https://github.com/sgorpi/audacity-plugins
Punch Copy and Punch Paste are a more advanced way of copying and pasting audio. It allows you to copy a larger selection (say your room tone) and paste it into a smaller selection (say a breath) without moving audio clips in relation (non ripple copy and paste). I guarantee you will find a use for this plug-in and incorporate it somehow into your workflow: https://forum.audacityteam.org/t/punch-copy-paste/28906
Not a plug-in, but adjacent. This is the spreadsheet that I use when submitting my audio to clients. It formats the data from an exported label file to be readable and paste-able into a message when uploading files to Discord. just make a copy a use for yourself: https://github.com/inimazade/VO-Timestamp-Compiler-for-Audacity-label-files-for-Discord-UploadabilityÂ