Happy to share some of what's been working for me. Some of this is stuff I'm actively using, some of it hasn't quite made it into the "day to day use" yet, but I've been experimenting with. (Random personal advice: Never let your note taking tools feel like using them is work, that's the first step towards not keeping notes!)
- For fans of "outline workflows" Outliner is excellent. A whole bunch of outline/indented text movement and manipulation commands: https://github.com/vslinko/obsidian-outliner
- For easily refactoring notes that are getting too large you want to have Note Refactor. It gives you tools to easily take blocks of text and quickly cut them out into new notes. Its not magic out of the box, but its a powerful tool you can use when building workflows with other plugins. https://github.com/lynchjames/note-refactor-obsidian
- Local images is another good one, working with online content can get messy when you copy notes and then want to be able to work any where you have Obsidian synched. I've got it on my Laptop, two desktops, phone and tablet... I want to carry as much of my related content with me so having an easy way to convert remote images to local copies is a big productivity boost when making notes about content from the internet. https://github.com/aleksey-rezvov/obsidian-local-images
- For analysing the content for some useful stats there's: https://github.com/SkepticMystic/graph-analysis but this is for a relatively specific sort of analysis.
- More general and flexible analysis and graph visualisations are available from the combination of https://github.com/zsviczian/excalibrain , https://github.com/blacksmithgu/obsidian-dataview and https://github.com/zsviczian/obsidian-excalidraw-plugin ... in short query your notes and note metadata like its a database, build reports and data visualisations, and then excalibrain is a whole thing built on top of that power.
- Dynamic embeds of outside content are available from https://github.com/dhamaniasad/obsidian-rich-links and https://github.com/Seraphli/obsidian-link-embed depending on the style and use you like. While there is a built in functionality to preview the links to other notes when you hover over them https://help.obsidian.md/Plugins/Page+preview which has a demo here https://youtu.be/dmnVml_jbsQ?t=222
- And a real force multiplier is adding https://github.com/Taitava/obsidian-shellcommands to your setup. It lets you run scripts and prompt for information and really invest time in procedural automation without having to build your own javascript plugins. So you can setup your system so that when you use the refactor to cut out a new note, the automations will trigger, ask you to give the note a new heading, tags, and you have a little script that checks last modified time of the folder tree of text files, and looks at the folder of the last modified time and asks you in that popup if you want to move the new note to the folder the note you cut it from is located in. Or anything else you can imagine using outside automation and scripting tools on your plain text markdown files.
These are just a start and if you haven't already browsed the plugins at https://obsidian.md/plugins I wholeheartedly recommend it, people are adding new cool things pretty often and other plugins add new functionality that makes them worth checking out if they were previously not something that you found interesting. I do a read through of the plugin list probably at least once every month or two just to see what's new, and more often if I'm experimenting with changes to my workflow.