While playing, press CTRL + SHIFT + C then type these cheats.

gold         ->  accrue 1000 gold
mana         ->  accrue 1000 mana
spells       ->  toggle free spells
research     ->  unlock all spells
win          ->  complete current level
lose         ->  fail current level
freemove     ->  toggle no movement cost
towns        ->  see all towns in map
explore      ->  toggle reveal all map
fog          ->  toggle fog layer
instantprod  ->  toggle fast build
instantres   ->  toggle fast research
ai           ->  toggle computer controlled force (yours)
cityspy      ->  toggle spying
upgradehero  ->  upgrades current hero
emergehero   ->  cast summon hero spell