Here is a tutorial on using Devmode in Portal:
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Cheat mode:
To use cheatmode(Devmode):

1) Enter the options menu, select "Controls", then "Advanced". Turn on the option for the console.
2) Press ~ during game play to display the console window.
3) Type sv_cheats 1 to enable cheat mode.
4) Enter one of the following codes at the console window to activate the corresponding cheat function.

Effect Codes:

Allow separate sets of portals to be created: change_portalgun_linkage_id <0>

Fire an energy ball: fire_energy_ball

Portal placement cannot be bumped: sv_portal_placement_never_bump 1

Portals can be placed on almost any surface: sv_portal_placement_never_fail 1

Allow use of second portal placement: upgrade_portalgun

Spawn citizen: npc_create npc_citizen

Spawn Breen: npc_create npc_breen

Spawn zombie: npc_create npc_zombie

Spawn Bouncy metal ball: ent_create_portal_metal_sphere

Spawn Weighted Storage Cube: ent_create_portal_weight_box

Basic portal gun: give_weapon_portalgun

First person view: firstperson

Third person view: thirdperson

Fire rocket from head (glitched): fire_rocket_projectile

All weapons, including those from Half Life 2: impulse 101

Invincibility: god

Take damage but cannot die: buddha

Set gravity; "600" is default: sv_gravity <number>

No clipping mode(means you can fly and go through walls): noclip

Disable cheat mode: sv_cheats 0
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Hoped that helped some of you

Impulse 101 was also a code in Counter-Strike Source... How odd.

Also, I didn't know that Portal was from the same makers as Half-Life... Makes sense when I think about the fact that they're sold together in The Orange Box, and both made by Valve... I'm so slow.

So, here's a question. Do CSS maps work in Portal as well, or only Portal and HL2 maps? I'd also love to rip the Portal gun and put it in CSS...it'd be even more awesome to manage to get that in Halo, but there's no way CE could handle nor support that...