As you all may well know cheating has recently become quite an issue with TeamFotress and QuakeWorld in general, due to the release of the QW source code. Access to this source code has allowed certain homosexuals to "hack" the qwcl and allow them to do some fucked up shit on QW servers. Of course cheats have existed since the beginning of QW and have come and gone as new versions of QW and TF have been released, but they have never been as effective as the newer ones.

Not Cheats

Bugs
Before we move on it should be pointed out that certain bugs exist in teamfortress that should be mentioned and explained so that there is no confusion between cheats. (Some of these are considered part of the QW physics rather than bugs - and should be thought of as such)

Friction "bug" - this is basically what allows one to bunnyhop or speedjump.
Sniper LED bug - this allows us to see the sniper dot of another sniper behind a wall. This is important to note for new snipers. as in maps such as 2fort5 they find themselves getting shot before they can see the enemy sniper. Its a bug that has been around since the beginning of TF so new snipers should learn to "hide their dot" rather than crying about it.
Map verticies - this is more a problem with a map rather than QW or TF. When a wall or ramp isnt alligned properly it may cause a player to get "stuck" like there is something invisible blocking them. An example of this is in the rock2 yard when walking along the edge from the flag entrance to the yard entrance .
Dispensers - Sometimes an engineer will build a dispenser at a certain part of a map and it will become invisible but is still there. It is rare but does happen.
Detpacks - Can be used as blockades on certain parts of maps. It is still argued whether it is a bug or is a normal part of TF.
Wallslide - Allow you to "stick" to the wall down lifts in maps such as bam4 and 2fort5.

Others
IdGamma - this increases the brightness of the quake pallete and therefore increases the brightness of the whole game. Its mainly designed for glquake and for graphics cards such as TNT's which are often too dull to play normally. It can also and often is used for software users also.
NF, Qizmo, Cheapo Proxies - Many associate the word proxy with the word cheat, so be carefull and dont jump to conclusions. These are mainly communicational proxies, and enhance teamplay greatly. They also have some other neat features such as wav file teamtalk messages etc. You can see who is using one of these by typing "f_version" in the console.
WaterVis - This is exclusive only to glquake users and allows them to see other players thru the water. It can only be used when the server allows vised maps.
DOX Mdl's - Eyecandy for TF in the shape of new weapons and other models. "f_version" will bring up altered models for proxy users. Don't assume altered models means cheating.
 

The Cheats

 --- Older Cheats (Prolly alot more than what is listed here) ---

Maphacks 
These are basically altered versions of maps which include invisible sections, and lightened areas. The most famous one was the original 2fort4 which had invisible cutouts on the sniper decks and the ramps. More common was fully lit maps (no shadows or dark areas). These are now ruled out since the sv_mapcheck was introduced as standard on servers. It runs a checksum on the client's map so if the map isnt exactly the same as the one on the server the user isnt allowed in. 
Some have mentioned that invisible maps are possible since the new source code was released but i don't know whether its possible or not. Any money says that some lame fat fuck who breaks into sweats when he moves the mouse is working on it.... penis in one hand pizza in the other.

Glow Skins
These are basically class skins that have been painted with lots of fullbright white so they can be "seen in the dark". Its only effective in software, and they look like engineers with labcoats and running skeletons etc. I dont know how people can tell the colour of the class with glowskins but they prolly just chuck and spam shit at anyone so it doesnt matter to them. You can usually tell if they use glow skins by checking user info and looking at the player's "pmodel" but its not always the case.

AA Proxies
These essentially did the aiming for the player, and put the crosshair on the enemy. Because of lag they were never effective for sniping unless the player had a low ping. These could be easily picked out by simply spectating the player. U'd have to be so unco to want to use one of these...if you think it helps maybe you should consider starcraft.

Radar Proxies
Basically the scout radar enabled on all classes. As u can imagine this would be an enormous advantage to have as it allows serious ass banditing by limpdicks that need a penis pump and 10 viagra tablets to get all 2 inches up.
 

Spiked Models
This I have not seen but I assume it would look like a model with a bunch of skewers thru him. It would allow the player to see where another player is thru a thin floor or thru a wall they are standing next to. People who use this most likely run round the corner with a primed gren while spanking off thinking how good they are.

--- Hacked Clients ---
People who use these are simply damaging TF and are in desperate need of a bullet. As far as I know only a few exist however there are prolly several dickless cocksucks with other ones.

Speed Hack
The speed cheat is the most obvious, and allows a player of any class to run over twice as fast as a scout (not speedjumping). Acceleration is almost instant and they are almost impossible to hit. I mean....how tiny must ur balls be to wanna use this?? One thing to look out for is people "tweaking" this cheat to give them a small percentage speed increase. These are lamers who know they arent good enought to make the cut so take performance enhancing drugs and hope no one finds out. 

Auto-aim
The other fag hacked client is Auto aim made by Gotwalls (Its possble gotwalls was hired by ID1 to push people away from qw and towards q3. As payment the Id1 people gave Gotwalls several days of asspumping and a copy of q3) Just spectate a player with cl_chasecam 1 and see if their dot follows a player or instantly snaps on b4 a shot. 

Examples of some pin dicks:    aacheat1.zip    aacheat2.zip

Air-Hang
Yet another one I've seen, but only once so far, is where the player is able to hang in midair for some period. The obvious translation for this action is "Look at me! I have no testicles and are proud of it!"