First, enable the console by going to Documents>BioWare>Mass Effect>Config on your computer. Then open BIOInput in Notepad. Find the line [Engine.Console] and under it add the line ConsoleKey=Tilde. Then when playing in game simply press the tilde key (above tab) to open the console, then type in the desired cheat.

Effect	Code
Add indicated number of credits into your account	initcredits [1-9999999]
Add indicated number of talent points for player	givetalentpoints [number]
Adjust credits plus or minus the amount entered	adjustcredits [+ or - 1-9999999]
All grenades	giveallgrenades [manufacturer name]
All human armor	giveallarmorhuman [manufacturer name]
All Krogan armor	giveallarmorkrogan [manufacturer name]
All Quarian armor	giveallarmorquarian [manufacturer name]
All Turian armor	giveallarmorturian [manufacturer name]
All weapons	giveallweapons [manufacturer name]
All weapons and armor mods	giveallxmods
Disable ghost and fly codes	walk
End game	quit
Flight mode when you climb stairs	fly
Get armor from indicated manufacturer	giveallarmor [manufacturer]
Get assault rifle that inflicts 25000 points of damage	givesupergun
Get Bioamps from indicated manufacturer	giveallbioamps [manufacturer]
Get indicated amount of experience points	givexp [number]
Get Omnitools from indicated manufacturer	giveallomnitools [manufacturer]
Get one of every weapon and modifier item level 1-X	giveall
Get the indicated talent, regardless of your character's class	givebonustalent [talent number]
Increase jump height of Mako ATV3	upgradevehicle [1-6] vehthrusterforcebooster
May increase armor value of Mako ATV	upgradevehicle [1-?] veharmorboost
Set paragon to indicated value	setparagon [number]
Set renegade to indicated value	setrenegade [number]
Show game settings	show
Spawn indicated item(See Note 1)	giveitem self [level 1-10] [type] [manufacturer]
Spawn indicated number of grenades2	initgrenades [1-5]
Spawn indicated number of Medigel doses2	initmedigel [1-5]
Spawn indicated number of Omnigel "doses"	initsalvage [1-999]
Suit of light "Survivor X" armor with 8000 shields	givesuperarmor
Teleport to pointer	teleport
Unlock the indicated achievement	unlockachievement [achievement number]
Walk through walls and fly	ghost

Note 1. For example, enter giveitem self 8 assault_rifle manf_ariake_weap to spawn a Ariake Technologies Tsumani VIII assault rifle. Note that the numerical value after giveitem self portion of the code represents the level of the item or weapons spawned.

Note 2. You normally can only have a maximum of five grenades or doses of Medigel in your inventory. However these maximums can be increased by changing entries in the "DefaultGame.ini" file.

Note 3. The Mako tends to take some damage upon landing from increased height. You will have to re-enable this code whenever you return to or from the Normandy, or anytime you land on a new planet.