In single player only, press enter to put in the code and it should say cheat enable if you entered a valid code.

Example: [Enter] greedisgood 100000 [Enter] Cheat Enabled!
Code Effect
WhoIsJohnGalt Enable research
keysersoze (value) Gold
iocainepowder Instant doom
somebodysetusupthebomb Instant Loss
thedudeabides Instant spell performance
allyourbasearebelongtous Instant Win
whosyourdaddy Invulnerability
motherland (race) (level number) Level select
leafittome (value) Lumber
greedisgood (value) Lumber and Gold
riseandshine Morning
lightsout Night
StrengthAndHonor No defeat
strengthandhonor Play after dying in campaign mode
TenthLevelTaurenChieftain Play the "Power of the Horde" song
whoisjohngalt Quick research
= Re-enters the last cheat code you typed.
sharpandshiny Research all upgrades
DaylightSavings (Insert Hour) Reset the time to the hour specificed (without a number, this toggle the day/night cycle on/off)
WarpTen Speeds up the construction of buildings and units
PointBreak Takes away the food limit
Infinite mana thereisnospoon
synergy Turn off Tech-Tree
itvexesme Turn off Victory
pointbreak Units need no farms
iseedeadpeople View entire map