some addons you will always use when modelling:
looptools already in blender
edit mesh tools already in blender
f2 already in blender
curve tools already in blender
add mesh extra objects already in blender
add curve extra objects already in blender
zaloopok Zaloopok "Shrink & Grow Edge Loops & Rings Selection" add-on
miratools MiraTools
interactive tools https://maxivz.gumroad.com/l/ynJmIV
forgotten tools Forgotten tools
machinetools (Free) and machinetools Deus Ex (Paid) MACHIN3tools
meshmachine (paid but definitively useful for semi non destructive mesh modelling and many other tools)
MESHmachine
Zen Sets (Paid addon for mainly storing selections, that cant be stored with the default vertex groups) Zen Sets for Blender
autodelete Auto Delete
connect edges Connect Edges
edgeflow https://github.com/BenjaminSauder/EdgeFlow
fast loop Fast Loop
KeKit tools keKit for Blender (2.8+)
modifier list Modifier List 1.7.3
modifier tools already in blender
for uv mapping uv-packmaster [UV Packmaster] Efficient UV packing solution for Blender (C++ based, multithreaded)
recommended but not required:
boxcutter
hardops
black mesh
beziermesh shaper
grid modeller
quad remesher addon