A cool cheat
You gotta try this one!
Replace (weapon) with any weapon like these: (The number is the default power so don't type it in yet)
Buckshot 5 (shotgun ammo)
Replace (skill) with the current difficulty level you play 1 = easy, 2 = normal, 3 = hard. This one is necessary.
Replace x with a number. The number you type in is the ammount of damage the weapon can cause. If you simply put in -sk_plr_(weapon)(skill) you will se the default power for the wepons.
It will look like this if you change the crowbar while playing on easy:
Note: Try replacing the power of the satchel with 100000000. Now take one out and detonate it. It will kill everyone and everything onscreen, even you unless you use god mode.
Note 2: Here's the coolest thing. Try replacing the power of the crowbar (10) with a negative number like -20. Now ask yourself: What happens if one causes negative damage to a target? Well, it will actually HEAL the target!! Amazing, huh? This way you can change the health of a target from their original energy to more than 10000 if you want to.