At ANY opening screen/menu, type in (version 1.0):

 iamcheater - (it's listed twice, so if once doesn't work, type it
              in twice.) You'll hear a click if entered correctly
 allitems - gives you all weapons with full ammo
 resurrect - same as what zombie was in the demo, brings you back to life
 goodhealth - gives you good health
 nohits - player doesn't take hits
 killthemall - kill all the enemies
 funnyhead - Big heads (I think)
 gamedone - successfully completes current mission
 gamefail - current mission ends in failure
 openalldoor - just like it says.. opens all the doors
 showtheend - I believe this shows the ending movie for the game.
              Use at yer own risc.
 laracroft - heh.
 enemyf - shows enemy in front of you.
 enemyb - shows enemy behind you (so you can see where/what they are doing).
 playercoords - your coordinates in the game.
 debugdrawvolumes - no idea what this does.
 debugdrawwire - wireframe mode (haven't tried it)
 quickload - loads the savegame of the current mission

 After the update the cheats have been crippled, now only work:

 iwillcheat   - Activate cheat mode
 goodhealth   - Life energy complete
 killthemall  - All enemies die
 missionover  - Jump to next mission

 ---

 If you have a censored version of H&D you can type in BLUESTARS and the
 games is uncensored. This works in versions 1.1 / 1.2 .