What are the cheats for League of Legends

There are no cheats for League of Legends.
The closest thing to a "cheat" was the Konami Code. (Which is now changed).

When you are in the launcher (the window that says if the servers are Online, Busy, or Unavailable), if it says Busy or Unavailable, press:

Left, Right, Left, Right, Down, Down, Up, Up, 3, 4

That's the Konami Code, with 3 4 at the end of it. If you press the combination correctly, it will show the servers as being online. You can then get into the Air window (the place where you queue up for matches, edit your masteries, etc.). This is local only, and will not actually get you onto the servers (they are Busy/Unavailable for a reason). This is used to test your own files while the servers are down. You still can edit your Runes and Masteries, and it will register the changes when the servers come back online. Another one is pressing Ctrl+L and type in javascript:setServerStatus(1)

This is the closest thing to a cheat in League of Legends. There are no cheats because the game is server based.
Editor addition: You can also type in "thereisnourflevel" if your client is showing Busy/Unavailable. This will make the server status go online.