Basic commands are listed here.  Commands can be entered by enabling the console which is pressing the ~ key (by defaulT)

>>Server Options:
These types of commands are generally called CVARS. The following CVARS are only accessible by the server. To find the status of a CVAR, enter its name. To change it, enter its name, leave a space, and then enter the new value. Note: some of these do not take effect until the round restarts.

mp_fadetoblack (default 0)
When set to 1, player's screen fades to black for the remainder of the round when he dies (hud still works normally so player can chat and see the scores, etc.) Overrides mp_forcechasecam

mp_buytime (default 1.5)
Designate the desired amount of buy time for each round. Min buy time is .5 minutes. No max buy time.

mp_winlimit (default 0)
Will cycle the map after one team reaches this many wins.

mp_limitteams (default 2)
Maximum number of players that one team can have over the other. To entirely disable team limiting, set to 0.

sv_restartround (default 0 sec)
Time until the game restarts fresh, or 0 to not restart. This will reset all frags, scores, weapons and money to default. Use this to coordinate clan matches.

mp_autokick (default 1)
Enable automatic team-killer banning and idle client kicking.

 

mp_autoteambalance (default 1)
Toggles auto balancing of teams.

 

mp_chasecam (default 0)
Limit observers to chase modes.

 

mp_c4timer (default 45 sec)
C4 timer duration. Minimum of 15, maximum of 90.

 

mp_freezetime (default 6 sec)
The length in seconds of the Freeze period at the beginning of rounds. Set to 0 to disable.

 

mp_roundtime (default 5 min)
Min round time is 1 min. Max round time is 9 min. Supports partial minutes (1.5 is 90 seconds).

 

mp_friendlyfire (default 0)
Set to 1 to enable friendly fire, 0 to disable.

 

mp_timelimit (default 0 min)
Period between map rotations.

 

mp_maxrounds (default 0)
Maximum number of rounds to be played on a map, leave at 0 to obey mp_timelimit.

 

mp_footsteps (default 1)
Set to 1 to enable footsteps, 0 to disable.

 

mp_flashlight (default 1)
Set to 1 to enable the use of flashlights, 0 to disable.

 

mp_tkpunish 0/1
if set to 1, TK'ers will sit out next round

mp_hostagepenalty X
X = max. number of hostages you can kill before the server boots you out... setting this to 0 will shut off this command

mp_logmessages 0/1
used for server admins to spit out chat messages in their log files

mp_forcechasecam 0/1/2
When set to 2, not allowed to spectate anyone...player's view stays where the player dies. When set to 1 only allowed to spectate player's own team when player dies. Default 0.

 

Client Options:
Anyone can use these to alter their personal settings.

cl_observercrosshair (default 1)
Set to 1 to enable crosshairs in Observer mode, 0 to disable.

cl_hidefrags (default 1)
Set to 1 to hide all frag/death counts on the Scoreboard but your own, 0 to show.

 

hud_centerid (default 0)
Set to 1 to center auto-ID text on screen, 0 to have auto-ID text in the bottom left corner.

 

lefthand (default 1)
Set to 1 to use left hand, 0 to use right.

 

max_shells X
X = maximum number of shells at one time

max_smokepuffs X
X = max. number of smoke puffs at one time

 

fastsprites X 
x = 0 : regular transparent smoke grenade sprites
x = 1 : simple transparent smoke grenade sprites (default)
x = 2 : VERY simple transparent smoke grenade sprites

 

adjust_crosshair
Each time you type this into the console your crosshair changes colour. There are 5 colours to choose from.

 

con_color
Change the colour of your HUD. Like con_color "256 256 256" numeric values can be found by looking in most paint packages.

 

timeleft 
Tells you how much time is left on the map

 

setinfo vgui_menus X
{X = 0 or 1, 0 disables VGUI menus, 1 enables VGUI menus}
(also available through the "Play CS" > "Customize" menu)

*Note: If the buy weapon system malfunctions, disable the vgui
through the "Play CS" > "Customize" menu

 

Infokey settings. Type "setinfo" to check the status of all infokey settings. To change one, type "setinfo <keyname> <value>". InfoKey Keynames dm (default 1)
Set to 1 to display map briefings after loading new levels, 0 to disable.

 

ah (default 1)
Set to 1 to enable auto-help, 0 to disable. Auto-help gives the player hint messages throughout the game.