sv_cheats 1 - Enables cheats (access to cheat commands)
sv_portal_placement_never_fail 1 - Allows portal placement everywhere

noclip - Toggles noclip
notarget - Makes player not visible to entities (ex. no target for the turrets)
changelevel (map name) - Changes to map
playgamesound (sound name) - Plays a sound from the game's files
impulse 100 - Enables flashlight
impulse 101 - (Portal 1) Get Half-Life 2 weapons
ent_create_portal_weighted_cube - Spawns a normal weighted cube
ent_create_portal_companion_cube - Spawns a companion cube
npc_create npc_personality_core - Spawns wheatley
npc_create npc_portal_turret_floor - Spawns a turret

cl_showfps 1 - Shows a FPS counter (not the Steam FPS counter)
r_decals 0 - Allows no decals (ex. no turret bullet holes)
r_shadows 0 - Disables shadows
mat_filterlightmaps 0 - Makes lighting pixelated
mat_picmip 10 - Makes textures low quality
mat_showlowresimage 1 - Makes textures REALLY low quality
cl_drawhud 0 - Disables the HUD and crosshair
mat_fullbright 1 - Makes everything bright