I've recently figured out how to port models from Valve's source games (Half Life, Team Fortress 2, Counter strike ect.) and a good deal of Garry's Mod model you can find.
Here's an example of a model I took out of Portal:
If you want an in-game shot
check this outRequired tools:
3dsmax 2011
The SMD importer plugin. The 2010 version works with 2011.
SteamA source game. I recommend Tf2, since its free.SourceSDK, you can download this with steam for free if you own one of Valve's major Source Games.
GFScape Only needed if you're ripping from a game yourself.
MDLdecompiler VTFEDIT for extracting materials.
Your favorite Hex editor.
Only read this part if you're extracting a model yourself
This next step may already be done, but its important you check anyway.
Open your .mdl file in a hex editor and make sure the character I highlighted below is a ",". (Tf2 models are 0 by default)
Open the mdldecompiler and input your model, and an output path, The model decomplier must be located in:
C:\Program Files (x86)\Steam\steamapps\*SteamUserName*\sourcesdk\bin\ep1\bin\ for it to work!
Export your model, and open 3DSmax 2011, and import the ".smd" file the MDLDecompliler makes.
Now for the textures, Open the .vtf files with VTFedit, and go File > Export, and chose whatever image format you want. Occasionally, you have to fight with the settings on VTFedit to get the entire texture.
Apply your texture in 3dsmax, export it as a .dae, and you're good to go.
I'll do .bsp files (maps) some other time.