Most likely these ideas have been said but here are my ideas.
this would turn off weather cycling, no more rain/thunder/snow/sunshine - whatever weather you were in when you turn this to false you would stay in until you change this to true.
this would cycle the choices of weather you want, in order from first to last and back to first.
in the above it would cycle rain/thunder/snow/clear and back to rain.
so you could have your custom map set up to cycle weather in a way that makes sense for your map
makes snow fall, pretty simple.
This would make samplename into a random number from 1 to 10 (or any number(s) you want)
you then could put samplename into other commands like this:
/tp @p ~samplename ~ ~
so whatever number was chosen for samplename that is where the player would get TP to.
this could be useful in lots of ways, randomizing is one of the hardest things in minecraft to really pull off and I think we need a simple command that does it.
One more menu screen:
I'd like to see the command blocks in the redstone category in creative, but I can understand the powers that be might not want new players to be confused by it maybe? So how about an "advanced" tab that has the command block, barrier block, and perhaps other blocks we used to be able to get (lava,water,portal) there could be an option that would start as set to off that would not show the advance command tab, and players that know about redstone and such could just turn that on - maybe in the main menu that would be a global effect for all your worlds. For multiplayer server's with creative mode on have a command that turns off the advanced tab for the admin, if they did not want players to use command blocks or whatever is in the advanced tab at all.
those are my humble suggestions sorry if they are repeats.