hey guys i think i found the best minecraft mod EVER. its for minecraft beta and i think right now its up to 1.4_01 update idk
well basicaly the mod is like haveing the multie player commands but its for single player mode. its called "single player commands mod" heres a video link that shows you how to install it http://www.youtube.com/watch?v=swWJjZI7dUU

here are the commands

ascend - Moves you to the next platform above your position
clear - Clears the console
defuse [all] - Defuses any TNT nearby which has been hit, drops 1 tnt in its place
descend - Moves you to the next platform below your position
destroy [all] - Destroys the current item
difficulty <LEVEL> - Sets the difficulty to the specified level (0-3)
duplicate [all] - Duplicates and drops the currently selected item stack
falldamage - Turns fall damage on/off
goto <NAME> - Goto a waypoint
heal <HEALTH> - Heals a player the specified number of points
health <min|max|infinite> - Sets the health of a player to pre-defined figures
help [COMMAND] - Gives general help when COMMAND isn't specified, gives specific help when COMMAND is specified. Same as /h
home – Teleport to spawn point
instantmine - Turns instant mining on/off
item <ITEMCODE> [QUANTITY] – Gives player item, if quantity isn’t specified maximum amount of that item. Same as /give and /i
itemstack <ITEMID> [QUANTITY] - Gives the player the specified quantity of maximum item stacks of the item.
jump - Moves you from where you are to where your mouse is pointing. Note: This command is buggy and may put you in the block you move to.
kill – Kills the current player
killnpc [all] - Kills all living creatures nearby.
listwaypoints - Lists all waypoints. Same as /l
music [VOLUME] - Requests a music track to be played, there is a limitation of at MAX 2 tracks per day. Set the volume by specifying VOLUME.
pos – Gives current player position. Same as /p
rem <NAME> - Removes the specified waypoint
repair [all] - Repairs the currently selected item to full health
return - Moves the player to the last position before teleport
set <NAME> - Mark a waypoint on the world
setjump [JUMP|reset] - Sets the height that you jump. Note: Turns fall damage off if the jump is configured to move than 1.
setspawn [<X> <Y> <Z>] – Set the current position as the spawn point, if X Y Z are specified sets that position as spawn point
setspeed [SPEED|reset] - Sets the speed that the player moves
spawn <CREATURENAME> - Spawns the specified creature a few blocks away from your current position (use "/spawn list" to get a list of creature names and codes).
tele <X> <Y> <Z> - Teleport to X Y Z coordinates. Same as /t
time [set|get|day|night [minute|hour|day [TIME]]] - Set and get the time within minecraft.