Are there any cheats for Left4Dead 2

If you're playing on the PC, yes.
First, to enable cheats, you have to enable the developer console. To do this, from the main menu, go to Options -> Keyboard -> Advanced -> Enable Developer Console

Then press the ~ key (It is directly below the Esc key and above Tab, to the left of 1.)

This opens the developer console.

To enable cheats, you type sv_cheats 1

NOTE: This will disable achievements until you restart the game!

Now, you can use the following cheats:

• god 1 - Enables "god" mode (don't take any damage)
• impulse 101 - Gives you full ammo and health.
• buddha 1 - Cannot die (never drop below 1 health)
• give <item name> - Gives you the item.

Some item names:

• rifle - M16 Assault Rifle
• rifle_desert
• rifle_ak47
• molatov
• pipe_bomb

Good luck!