Everyone knows the minecraft commands like /toggledownfall /time set day and things like that. For other commands download Single player commands! Look it up on Google, click the first option, which should bring you to minecraftforum.net. Scroll down until you see the download for your operating system, Mac, Windows, Linux. Now there are 2 blue underlined buttons. Manual and Preferred. Click preferred and it should begin to download in the 'downloads folder.' Once it's done, drag it to your desktop. Double click it to launch it. It will open a window with a long command in a box. Like this: users/BillDoe/applicationsupport/minecraft so on. There should be 2 boxes: Back up Minecraft.jar and Back up worlds. Check the Minecraft.jar. Hit Install and it will load then, soon, say complete.
Launch Minecraft. Open a world. It should say about single player commands 1.4.7. Do /help. A VERY LARGE list will come up.
Now you should have stuff like:
/forestgen
//removeabove
/thaw
/thru (teleports you through walls, doors,roofs... As long as there is an open space on the other side.
All kinds of good stuff!

DISCLAIMER* Single Player Commands is BLOCKED on almost all servers.

From me here at Nate_The_Doctor Industries... Go Wild!