This mod by Team John is a modification of gmod with a mega amount of extra stuff added to it to make it better.
This mod from MeliorMultimedia is a virtual photo gallery. You can walk around with your friends and family and view people's pictures.
GamersHell:
Fortress Forever is a Team Fortress mod for Half-life 2's Source Engine which expands on the classic Team Fortress action as well as introducing elements to improve accessibility for players new to the genre. Half-Life 2 - Fortress Forever features nine classes, 10 core maps and 6 different game modes centering around Capture The Flag, and Capture and Defend gameplay.
This mod by pistoccoisdaman is a campaign mod. You wake up in a cell, Nova Prospect. You escape and go back to your apartment to find your family murdered and you have been framed.
This mod from -Lord- is the sequel to the Ravenholm mod. Picking up the story after John's escape from Ravenholm, you will visit new locations and meet new characters as you are taken prisoner by the Combine in City 24 and are reunited with an old friend.
This mod by InterWave Studios promises to bring all the best from the Stargate Movie and TV-Shows into the gaming world. The mod will have Multiplayer gameplay focusing on ground combat.
PC World: "So a fat pig jumps into my cab, and then he busts out into song while I carve through city streets. Nope, this isn't some deleted scene from the end of Slumdog Millionaire. I'm playing Karma Cab--a goofball mod for Half-Life 2.
Bit-Tech reports: "This is why PC gaming is better than console gaming in our opinion; because of excellent mods like this which keep on improving on the games we all know and love.
If you're thinking of buying the PC version of Left 4 Dead, you might want to look into purchasing the new Valve Complete Pack off Steam. In addition to L4D, the $100 package comes with both Half-Life games and a slew of additional content for each.