All of the following use the playersonly code in order to freeze the game. Since you cannot change weapons while the code is enabled you have to pre-select it. Most of these tricks also have a certain amount of "backlash" so the god code is also recommended. Some of these tricks require a lot of ammunition, so the allammo code should also be used. Once you are finished setting up the kill, move the console out of the way so you can see what happens then deactivate the playersonly code.

Sniper Rifle: Find someone to shoot, line up a head shot and fire. The target's head will become suspended in mid-air with a cloud of blood underneath and the body will fall to the ground. Note: Try to avoid zooming in as the game will occasionally freeze in the zoomed mode until you deactivate the code.
Rocket Launcher: When you use either primary or secondary fire, the gun will automatically load up six missiles and fire them. However, the rockets will stay where you fired them, resulting in them staying grouped. This allows you to run up to an opponent and surround them with groups of missiles.
Ripper: Hold [Fire] and run around randomly in an opponent's general area until he/she/it is surrounded by as many Razors as desired (usually about 50-60). Re-enter the code and clear the area as the Razors ricochet about and cut your opponent to ribbons.
Ripper: As above, only more tidy and less random. Face the direction your opponent is running. Aim the Ripper at the target's feet and hold [Primary Fire]. Begin to move the mouse very slowly up in a straight line, creating a "stacking" effect.
Redeemer: Enable the allammo code to get 999 missiles. Freeze time, then enable the fly code. Start flying around the level with [Primary Fire] held before reactivating time stop and consider the scale of the virtual pain your about to cause. Then start time and watch the fireworks. Note: Inspect a missile to find something interesting written on it. If you use this trick on a relatively large scale the game will slow down a lot, even on the fastest computers.