From SA-MP Wiki
This article contains a list of all the default SA:MP commands, and information about them.
/quit and /q
This command speaks for itself, it quits the game. You can also use /q, as it the exact same command, just shorter.
/save is most likley the most commonly used default command, and probably the most useful. When you type /save, your current position is saved to savedpositions.txt in your user files directory, from where you can use it in scripts.
/rs (Raw Save) is like /save, but it only saves your current position and facing angle in rawpositions.txt in your user files directory. No extra information is saved.
Partly as important as /save, this command simply displays your current interior in chat.
This command sets the limit of FPS (Frames Per Second) for your game. The higher the limit the smoother your game is. Has no effect if frame limiter is turned off in graphic options.
This command is used to execute RCON commands. RCON is the default admin system. RCON stands for Remote Control.
/pagesize is used to choose the amount of lines of chat to show. This can be anything from 10 to 20 lines. Pagesize is 10 by default.
This command will enable/disable the players head movements, however it is handled locally so other players will still see your head move.
This command will show/hide a time next to all messages in the chatbox.
DL stands for debug labels, this command toggles debug labels on vehicles, which show the vehicle ID, model, health, whether the vehicle is pre-loaded, distance from the player, trailer, available seats, current position and spawn position.
This command was added in 0.3x. When enabled (which it is by default), players will see a small hourglass icon next to the nametag of paused players. This includes minimising (alt-tab), the pause menu (ESC), lost connection (crash/timeout) and when taking screenshots that freeze the game for over 3 seconds.