Add the "+set developer 1 +set sv_cheats 1" command line parameter. Press ~ during game play to bring down the console window.

Spawn item: give (item)
Full health: give health
Save game: savegame
Load saved game: loadgame
Get all items: give all
Ammunition: give ammo
Invincibility: god
Ignored by enemy: notarget
No clipping: noclip
Fly mode: ufo
Teleport to a specific map node jumptonode
Play indicated map: map (map name)
Suicide: kill