I'll tell you mine and the story that goes along with it.

I have beaten the first eight worlds and am now in the process of collecting all of the Star Coins and finding all of the Secret Goals.  During this process of collecting Star Coins, I have experienced my greatest amount of enjoyment while playing this game. It was when I snagged the deviously placed coin in World 2-1.  It's the one where you are supposed to jump quickly on sand fountains while hopping onto a flying Koopa, grabbing him in shell form, and chucking him into the Star Coin that resides in the unreachable abyss down below.  This is how you are supposed to do it...

The way that I did it was different.  After trying to do this several times I saw a lost Toad show up at that world.  For those who don't know, there is a side quest in the game where you can find a lost Toad in a level that is hiding in a block and bring him to the end of the level to get a "surprise".  On the selection screen for the levels his face comes up in a cartoon bubble and screams out, "Help me!!!"  in a annoyingly high pitched voice.  This is when I came up with a briiliant idea.  I started the level and carried him almost all the way to the end of it.  This time I ignored the flying Koopa and jumped safely to a ledge on the other side of the seemingly unreachable Star Coin.  Then I took that annoyingly high pitched Toad and hurled him into it.  What a great moment of satisfaction.  I got the Star Coin and killed the aggravating Toad all in one great moment.  My greatest moment while playig NSMB Wii.

So what has been your greatest moment while playing this game?    

Probably when I got the secret exit in that windy level in world 2 unintentionally. I was just jumping at what I thout were appropriate times and I nailled it without realising it was even there. That made me feel awesome.

Nevermind, I haven't played Wii version of nsmb. :P

It's not a version.... this is just a semantics thing but you wouldn't say "Nevermind, I haven't played the 2nd version of Gears of War" when you mean GeoW 2.

"Version" is used for things like "gold version" of pokemon, or "Wii version" of Resident Evil 4.... not when talking about sequels that have entirely different content.

my greatest moment was in multiplayer.when i was playing with a friend and i do not remember in which level but we were stuck in a part and we were falling all the time.i took him in my strong mario arms and caried him all the way to the other side and at the end he jumped on me and made me lose!we laughed for hours.

I would like to repeat exactly what TWRoO said.  New Super Mario Bros. Wii and New Super Mario Bros. are two completely different games.  It's unfortuanate that some people don't realize this because they have such similar names.

These big spikes in some castles. Dude that was scary haha. The first level on world eight that had that black cloud following you too.

Plus the first battle against Bowser was quite nostalgic, and his comeback was remarkable.