Here are mine, I primary focus on low poly models by baking from high poly ones for games and use tools that make that workflow easier (and more fun):
Maya Config for Blender 2.8 - I come from a Maya background and this keymap add-on really saves the day for me. The author has been updating it often with more features and functionality which has been great. I almost feel like I am using a super version of maya with this add-on since I don’t have to fumble around learning new controls and can smoothly navigate in Blender 2.8 with maya navigation that I am so used to for many years.
OpenVDb Remesh - Hands down the best modeling add-on for me. I only stumbled upon it like 2 weeks ago when I was trying to find a similar method to converting low poly models to a high poly voxel (how I did with 3D Coat for years) and this tool felt like it was made for me. It works so great and can create awesome high poly models from low poly meshes with perfect bevels. It speeds up my workflow and is so hassle free I’m amazed how well it can convert my low poly meshes that have booleans or are just joined objects into one single cleanly beveled high poly mesh. Many nights for fun I will do a very quick 15 min model where I extrude, join, and add crazy booleans to it and then convert it with open VDB remsh. I am always amazed how it makes the low poly model into a high poly masterpiece in seconds that are ready to bake. Gone are the days of having to subdivide with edge loops. Converting a low poly to a voxel and instantly back to a high poly mesh all within Blender 2.8 is the way to go. The only downside to the tool is I fear the day it no longer exists or doesn’t work for Blender, I’d have to keep a version around JUST for this tool its that great for me. I wish the author could get it integrated as a feature to blender I love it that much.
Pie Menu Editor - What can I say I love customization and on top of it being able to make unlimited menus and pie menus of my workflow process has been a lifesaver. Hotkeys are great but with every add-on it means learning more hotkeys to the point it feels like a pop quiz every time I open blender trying to remember how I keymapped them all. I don’t have to do that with custom menus. I’ve created multiple pie menus for example, one with all my favorite low poly modeling tools, a high poly one, cleanup, and an adjustments pie menu (I am sure I will make more as time goes by). One bonus feature that makes me love this add-on even more is the ability to add custom icons for every menu option. I’ve created an entire pack of custom icons so all my menu options can be easily distinguishable and fit my custom theme colors for blender.
Machin3tools - Has a ton of great features to increase workflow and also makes certain modeling aspects a lot easier to do. One of my favorite features is the ability to be able to focus and isolate an object and then with the same hotkey revert back to the whole scene. The smart face action is also really great and makes filling holes in a mesh a lot quicker too.
MeshMachine - Easily my most anticipated add-ons to come to Blender 2.8. It has a ton of great tools to cleanup messy models, revert modeling topology that would otherwise take forever to do, and even more versatile ways to add things such as bevels with ease.
Fluent - A really great non-destructive boolean modeling add-on. It is pretty new and I have no doubt with more updates it will grow to be very powerful. It already it has a lot of great features to make modeling with booleans a lot less permanent and a way to always make changes on the go. It can save the worry and stress about messing up your model with boolean operations until you want to fully commit which is really great.
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I’ve only been using blender for a little while but already with add-ons have a great arsenal of tools that makes modeling so easy. It almost feels like cheating at times due to the countless amount of operations that either can skip tedious steps or make the workflow just simply faster with a tool that does something with a lot less manual work. Here are a few notable mentions of other add-ons I use that I like:
Make Line Tool (Included in blender add-ons) - A better version of the knife tool in my opinion.
Oscurant Tools (Included in blender add-ons) - I really love the distribute objects options, if anyone knows of any add-ons that allow more ways to distribute objects evenly in different patterns would love to see it.
Merge Tool - Makes merging verticies a lot easier and more fun.
Destructive Extrude - I love extrusion add-ons and this one is no exception. Being able to extrude inward on an object and it redoes the mesh without having to manually clean up verticies is very nice.
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I am sure as time goes by I will find even more cool ones to add that I can’t wait to try out. While I’ve not personally got to use the ones below yet they look really awesome and I will purchase them eventually:
Hard Ops and BoxCutter - Definitely want to get this add-on eventually. All the modeling and boolean methods to make models quick looks really awesome.
RetopoFlow - Looks extremely useful for retopology or organic objects. Can’t wait to see it come to Blender 2.8 when they port it over eventually.
Curves to Mesh - Really want to give this one a try one day. Looks like a great way to easily create clean topology for organic objects on my hard surface models like cloth, straps, etc.
Corner Extrude - Has a cool way to extrude for corners, would save a lot of time for sure.
Zig Zag Extrude - Another cool way to extrude from an object to create more complex shapes with far less steps involved.
Updated: February 4, 2024 ─ Added some add-ons
Order = alphabetical 
Great material library, predominantly free.
