Garry's Mod, and S-Mod (the tactical weapons are fun, also putting on bullettime (slow-mo) is AWSOME!!)
Eternal Silence is that space thingy right? s'not bad... kinda like starwars battlefront except psuedo turn based. also apparently those players haven't heard of EK either (which is supported in the game) bombing runs and strafing an enemy fighter is easy, and they normally miss you if they try to shoot you.
Dystopia Mod, hands-down my favorite Source mod. Cyberpunk galore with a twist of Tron, it has a somewhat steep learning curve but absolutely fun when you get the hang of it.
In a close second is Neo-Tokyo, a particularly fun mod especially if you are into Ghost in the Shell.
Maybe some day, they'll see a hero is just a man who knowshe's free.
Its not a HL2 mod but its HL 1 mod, ESF (earths special force) a dragonball z fighting mod
its okey if you have a lan of it or just want to beat people to a pulp