This is a list of fun commands to use with friends or bots, sv_cheats 1 might be required for most of them.
host_timescale (default is 1): Speed. If you raise it to 2, the speed of everything will be multiplied by 2.
sv_infinite_ammo (default is 0): Infinite ammo.
sv_gravity (default is 800): Change the gravity. Higher will make you fall quicker, lower will make you fall slower.
r_drawothermodels (default is 1): Wallhack. Set to 2 to see players through walls. (You can't do this on public servers, so it is safe, it will not get you vac banned. This is in no way a cheat.)
mat_wireframe (default is 0): Set to 1 to see through walls. More useful version of drawothermodels. This will not get you banned either.
weapon_recoil_scale (default is 2): Set to 0 for no recoil.
noclip (no default / toggle): Write it into console to fly, go through walls and be invincible.
god (no default / toggle): Become invincible.
give (no default): Use as "Give weapon_ak47" to give yourself an ak47. Full list of give commands here
thirdperson (default is firstperson): See yourself in third person view.
sv_showimpacts (default is 0): Set to 1 to see where you hit. Great for learning to control recoil.
These are all the ones I have for now, but I'll probably add more