This absolute command takes 6 screenshots in-game to make a sky background out of an in-game scene.
 

Report on total number of texels uploaded to the 3D card.
 

This enables/disables logging of GL commands.
 

This dumps a list of models currently referenced by the engine (not really useful unless you're making a full-blown mod).
 

This is a lighting direction vector for outdoor lighting as it applies to characters (scientist, player, etc) in the game. In daylight and outdoors, for example, higher values would result in darker shades in areas of character's body not hit by sunlight.
 

This is the color of the outdoor light vector.
 

This controls the color and brightness of tracer effects (that come out of the 9mm machine gun). For example, set "tracerred 2" and the tracer will look more reddish (cool and is my setting).
 

This command sends an update from a server to the master server (updates your server's info in the InternetGames menu). Yes, this isn't graphics related but I received a lot of queries on this. And they thought this turns on a heartbeat sound !!!
 

This turns on/off "gait estimation" which is used to interpolate other players' positions & animation during a multiplayer game.Again, not graphics-related but a lot of people thought this has to do with a single-player "bob".
 

The frequency with which you can spray your logo/decal. Default is 30 (seconds) which means you gotta wait 30 seconds between each spraying.
Change it to 1 and you'll be able to spray every one second. Works in both single-play or deathmatch.
 

Field of view. Default is 90. Higher number means you'll see more where you're facing and vice-versa.
 

Well, these are all grouped together as they provide and is relevant to having a thirdperson gamemode. All work on-the-fly. The last three cam_ cvars are my preferences for setting camera angles. Since these do affect visuals I'm including them here.
 

NOTE : THIS IS NOT FOR OPENGL, ONLY FOR SOFTWARE MODE (yes, useless if you run the game with the Voodoo2 but....)
Well, with the above notation, I include this primarily for those who are wondering what primitives Half-Life uses (fymfi, Half-Life uses triangles as well as quadrilaterals).
Setting to "1" (IN SOFTWARE MODE I remind you) will let you see the individual polygons of the world.
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NOTE : THE PARTICULAR VALUES ARE NOT FOR OPENGL, ONLY FOR SOFTWARE MODE.
Okay, this might be useful for mappers.
Setting to "3" means only lightmaps but with offset grid.
Setting to "4" is like "3" but would also show the mip level of each surface relative to the player.
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Screenshots:
Map in Anomalous Materials
Notice the weapon, the floor area where the lights are and all surfaces

r_fullbright 3	r_fullbright 4

Controls drawing of entities/models.
0 = no entities
1 = Default and draws entities normally
2 = entities drawn as skeletons
3 = entities drawn each bone having a bounding box
4 = entities drawn with box
5 = individual box for player and weapon NOTE: works only in SOFTWARE-mode

Screenshots:
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r_drawentities 2	r_drawentities 3
r_drawentities 4	r_drawentities 5 (software only)

There is a distance bug in the engine that sometimes causes the player to be able to "see through" distant walls or surfaces. Not sure if Valve will fix this. For the moment the best thing to do is to ensure distant walls/surfaces has a thick brush. Or you could try turning off gl_ztrick. If that doesn't fix it, it's because there is only a 16-bit Z-buffer on the Voodoo2(assuming you map-creators use one). If it happens in software, it's because there is only a 16-bit Z-buffer in the software renderer. For GL, you can try fixing it by getting a card with 24 or 32-bit Z (which means Voodoos need not apply L).
In software I don't think it's very noticeable.
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One of the things about the game that I found frustrating are the almost nondescript crosshairs for all weapons. This sucked big in bright areas of the game and especially so in deathmatch. So I decided I wanted the crosshairs to be more visible, bigger but without impeding on sight of target.
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You can get them here -- my modified crosshairs for all weapons. I bet your frag counts will increase J
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Some screenshots on the crosshair for the gauss weapon as an example :

Half-Life's Default crosshair	)))Reverend((('s crosshair

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NOTE : Make sure you enable the crosshair either through the in-game's Controls/Advanced Controls menu or by typing crosshair 1 at the console._
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