Start game, then bring down the console by pressing ~ aka tilde or ', then enter the code from below for the desired effect.

gamestop = Units gets 10% cheaper (only works in campaign mode)
oliphaunt = Elephants gets 40% bigger (only works in campaign mode)
Jericho = Walls fall down in a seige (only in Battle map mode)
For parameters that need more than one word (i.e a name) you must add between " (quotes) like "Mr Cheater".
bestbuy = Units become cheaper to recruit
toggle_fow = Toggles the FOG OF WAR
toggle_restrictcam = toggles camera restrictions
give_trait = gives the character a trait at level (default = level 1) for a full list of traits refer to gamedir\persistent_logs\issued_traits.txt. Theres a nice table after a list of crap at the start that shows them all.
list_traits = List all traits
give_trait_points = Gives the character points for trait. Basically used the same way as the give_trait command
give_ancillary = gives the character an ancillary for a full list of ancillary refer to gamedir\persistent_logs\issued_ancillaries.txt
list_ancillaries = List all ancillaries
process_cq = Completes all constructions in settlement thats in the queue
add_money = Adds money to the faction
add_population = adds an amount of population to a settlement, can be negative.
auto_win = the attacker or defender wins the next autoresolved battle
character_reset = resets the character back to its start of turn settings
show_cursorstat = shows the cursor position and region id
mp = Give the character movement points
list_characters = List all the characters that belong in the faction
filter_coastlines = applies filter to world map coastlines
toggle_coastlines = toggles strategy map coastline display
set_building_health = sets health of a building of the specified type (eg core_building) in a settlement, so that the final health percentage is as specified; for building chains see export_descr_building.txt
ai_turn_speed = sets the maximum speed of turn processing during the ai round
set_ranking_interval = sets the denominator of the faction ranking graph interval which is calculated as (number_of_turns / denominator). If set to 0, then the denominator will be set to number_of_turns, giving an interval of 1
regenerate_radar = Does what it says on the tin
toggle_perfect_spy = toggles everyones spying ability to perfect and infinite range, and off again
building_debug = toggles building debug mode. TAB to toggle view modes, RIGHT SHIFT-TAB to reset mode, LEFT SHIFT-TAB to go back modes. G damages mouse-over building. P displays plaza.
process_rq = Completes all (possible) recruitment pending in queue
force_diplomacy = Forces the negotiator to accept or decline a proposition
diplomatic_stance = Set the diplomatic stance between the two factions
invulnerable_general = makes that named general invulnerable in battle
burn_piggies_burn = ignite all the piggy winks
puppify_my_love = ?????
list_units = lists all of the units in an army, with details.
damage_wall = Damage wall of settlement. Forces 40% damage to a random gatehouse and a nearby straight section.
kill_faction = removes the faction from the game
kill_character = Kills the character
create_building = creates a building of the specified type in a settlement; for building level ids see export_descr_building.txt
capture_settlement = evicts any resident characters and armies and gives the settlement to the local