Some of these cheats involve editing game files. MAKE BACKUPS! You've been warned.
Unlock all factions:
Find this directory:
Medieval II Total War\data\world\maps\campaign\imperial_campaign
Then find the file descr_strat. Open it with a text editor. Cut and Paste the 'unlockable' section into the 'playable' section and save the file. Launch the game and you should have every faction available.
||Sometimes allows a character to move again
|add_population "settlement name" "amount"
||Add population to a city
|give_trait "character" "trait" "level number"
||Gives any trait your faction can have to a specific general
|process_cq "settlement name"
||Finishes everything in building queue for indicated city
||Gives you the specific amount of gold
||Shows coordinates under mousecursor in format x,y
||Toggles fog of war for entire world map
||Enter at the battle scroll for instant attack/defense wins
|move_character z x,y
||z=name of settlement or unit without title (except Captain). x,y=coords
Thanks to Revolution Reader ssj17346, redlights, and MANTIS!