Left 4 Dead Console Codes

I decided to put some of my favorite console codes for L4D into a post, both for my own future reference, and for anyone else who happens upon this post.

Type "sv_cheats 1" in the console to turn cheats on (NOTE: Turning cheats on will disable achievements).

Fly mode/Noclip
noclip

Third Person View
thirdperson

Over-the-Shoulder View
thirdpersonshoulder

Change Level
changelevel

Spawn Zombie
z_spawn

Play as zombies in Singleplayer
sv_cheats 1;
director_force_versus_start;
director_no_human_zombies 0;
sb_all_bot_team 1;
Press the "M" key to switch teams.

Check Achievement Progress
achievement_status

And finally, how to play the game in Splitscreen on the same PC.