Map pack addon - Garrys Mod for Half-Life 2 - ModDB

A mappack for Garrys mod 9 various maps and also a few vehicles. Inside the archive are other archives from where the different maps only have to be extracted into your \gmod9\ directory.

Gmod-Mod-Pack 2 addon - Garrys Mod for Half-Life 2 - Mod DB

Realistic Half Life: Source Sweps addon - Garry's Mod - IndieDB

Custom Maps and Mods for Garry's Mod

Steam Workshop::Realism Mods

Half Life 2 Nova Prospekt Prisoners NPCs addon - Garrys Mod for Half-Life 2 - ModDB

Make Garry's Mod Realistic with Add-ons! - Game Servers Rental

You can run Half Life 2 in VR through Garry's Mod : r/virtualreality

Garry's Mod Map Pack #19 (Map) for Garry's Mod

Garry's Mod, Half-Life Wiki

This Mod Makes Combine SCARY Strong (Improved Combine NPCs)