[Tutorial] The Portal Glitch Bible
Would ask for this to be stickied, or deleted if for some reason no one likes it.
Portal, based on the half-life 2 engine, is one of the greatest games of this generation, and many would argue of all time. The game is fun, challenging, and can be played for long hours at a time. The games uniqueness brings about a number of glitches that are used by both speed runners and casual players alike.
I'm putting this list in order of ease of use, and I'll include demos in chambers from the original game.
Portal Bumping: Portal bumping is probably one the most useful of all portal glitches, as it has a tendency to be over looked by map makers. Portal bumping is when you use a portal placed on a surface, to force a second portal through an otherwise un-passable object or surface.
Portal Standing: Portal standing is another very simple technique that you might have never realized you used! Portal standing, simply put, is when you shoot a new portal while standing in the old one. Crouching actually makes this a lot easier (I find) because you move less while crouching. Again, check out the demo if your unsure what I'm talking about.
Portal Peeking: This is a quite a bit like standing, except instead you use an already placed portal to shoot the next one, without actually being where you were...that's one hell of a sentence. You would use this technique if you want to have a portal between two places that you can't physically see.
Accelerated Back Hopping (ABH): This is a very common speed running technique that comes from the HL2 engine. You achieve ABH by bunny hopping backwards, some people claim you need to do a 180 in the air, but this is not the case. When you ABH, you don't hold backwards (S in most cases), and the bunny hopping aspect comes from either a script or manual input.
Item Climbing: This one is hard to explain, but in essence, it stems from the fact that you can stand on items. It's achieved by standing on an item, jumping, while in the air, grabbing the item (so it comes up to your feet), jumping off of it again, and repeating. Scripts are very commonly used for this feat.
Edge Glitching: Edge glitching is another example of forcing yourself places. Instead of portals, this time were forcing ourselves places. Basically, you have the edge of a portal up against a wall, and the equivalent edge of the other portal on an edge. You approach the second portal from the side, and you have the ability to shoot a portal into the room...or lack there of on the other side.
REALLLY STUPID GLITCH
To use this glitch, you need to go to the console and type 'kill'. You will instantly win the game. ~By Pestchamber
Demos: They are named for what they represent.
http://files.filefront.com/13758574
http://www.megaupload.com/?d=4PFC6Y7Z
I didn't include info nor demos on OOB nor the Save/Load perspective glitch (since I frankly don't know how the save/load glitch works, and this site has a hatred of OOB). I will add though, that youtube is your best bet for either of them.
[Updated with a new mirror]
I know this technique under the term "Portal Tunneling" which seems more recently used 
Thank you for the demos
//aaah, I am getting "Your download has failed. There were no available download servers.
Click here to try your download again."
Would you mind posting a mirror on some more reliable server?
(percentage calculation sphere self-test failed!)
108.1% done, -8.1% remaining...
Released here!
All maps for Portal (1/2) worth playing are mirrored here.
I would classify portal standing and portal peeking as tunneling, based on how they are described. Portal standing to me would be when you have two portals placed on a wall, such that neither are on the ground, and you can stand in between portals (on a surface that is not really there). You can then use this to tunnel.
If we post any glitches will you add them to the main post?
These are the primary engine based glitches, I don't think it would be good to post like... chamber specific ones? But hell, if you guys want that sure I'll do it.
And is that what the hell you guys have been talking about with "portal tunneling"? I've never herd it called that until I discovered this website.
I laughed my head off in chamber 15 when I got all the chairs 
I cannot manage to do ABHing. Do you need to be holding something? if so, would a security camera work?
I always heard Portal Peeking refered to as Portal Popping. Same thing I guess. I don't know if I would consider that a glitch though. It takes time for a portal to travel to the surface you shot it at and to form. If a player can re-enter an existing portal before that happens "Pop back through" why would it be a glitch?
Love these exploits.
I cannot manage to do ABHing. Do you need to be holding something? if so, would a security camera work?
Nope, your most likely having trouble with the bunny hopping part. You need to jump again before you actually hit the ground, try binding jump to your down mouse wheel. (bind mwheeldown +jump).
It's arguable. A glitch is anything the dev's didn't "intend" for you to do. Peeking and Standing are generally considered one in the same, and Standing is a glitch. *shrug*
Pest, out of curiosity, what did you have in mind?
Nothing. But if any of us found a glitch which is not listed in the main post and we go like
REALLLY STUPID GLITCH
To use this glitch, you need to go to the console and type 'kill'. You will instantly win the game.
(ofc something serious)
Would you add it to the main post?