In these FGDs I removed a lot of unused HL2 stuff (like turrets).
I improved standard settings of a lot of entities.
For example env_projected_texture or env_energy_ball_launcher
There are also some new entities, for example prop_exploding_futbol or prop_futbol.

Credits go to turk645 for following entities:
prop_glass_futbol_spawner
prop_glass_futbol_socket
prop_exploding_futbol_spawner
prop_exploding_futbol_socket

Newest entry: prop_glass_futbol

Put all 4 .fgd files to Steam\steamapps\common\portal 2\bin\

File Name: Improved_FGDs_4.zip
File Size: 124.01 KiB

Click here to download Improved FGD files

&

Updated the FGD's. Many improved settings included.

New update:
Added env_global entry to spawn without Portalgun (SP and MP). HL2 entries removed.
If you got any other Portal 2 relating env_global entry, post them and I will add them!

Update to V4:
Added prop_glass_futbol and set keyvalues of prop_exploding_futbol to standard prop_physics keyvalues.

You should add the prop_scaled_cube entity from the Sixense DLC. Here's some FGD code based on the prop_weighted_cube:

@PointClass base(Targetname,Angles, Reflection) studio( "models/props_underground/underground_weighted_cube.mdl" ) = prop_scaled_cube : "Scalable Cube"
[
   skin(choices) : "Skin (OLD)" : 0 =
   [
      0 : "Standard"
      1 : "Companion"
      2 : "Standard Activated"
      3 : "Reflective"
      4 : "Sphere"
      5 : "Antique"
   ]

   CubeType(choices) : "Cube Type" : 0 =
   [
      0 : "Standard"
      1 : "Companion"
      2 : "Reflective"
      3 : "Sphere"
      4 : "Antique"
   ]

   SkinType(choices) : "Skin Type" : 0 =
   [
      0 : "Clean"
      1 : "Rusted"
   ]

   PaintPower(choices) : "Paint Power" : 4 :
   "The paint power of the cube." =
   [
      0 : "Bounce"
      2 : "Speed"
      3 : "Portal"
      4 : "None"
   ]

   NewSkins(boolean) : "Use new skins" : 0 : "Use the values in the Cube Type and Skin Type fields instead of the Skin(OLD) field."

   allowfunnel(boolean) : "Allow Portal Funneling" : 1 : "Whether or not this object should auto-funnel into a portal."

   input  EnablePortalFunnel(void) : "Enable portal funneling behavior."
   input  DisablePortalFunnel(void) : "Disable portal funneling behavior."

   input  Dissolve(void) : "Dissolves the cube."
   input  SilentDissolve(void) : "Kills the cube and fires its OnFizzled output."
   input  PreDissolveJoke(void) : "GLaDOS make a funny about the cube."
   input  ExitDisabledState(void) : "Exits the disabled state of a reflective cube."
   output OnFizzled(void) : "Fired when a cube is fizzled."
   output OnOrangePickUp(void) : "Orange picked up the cube."
   output OnBluePickUp(void) : "Blue picked up the cube."
   output OnPlayerPickup(void) : "Player picked up the cube."
   output OnPhysGunDrop(void) : "Player dropped the cube."
   output OnPainted(void) : "Cube got painted."
]

Edit: Actually, that DLC has its own FGD.