I wanted to look for these anyway, but I thought that I would post up the cheat here, too. The games is so much fun, and I wanted to see what else you can unlock. So…. Here are some of the cheats I found on IGN.

Here is the page.

Unlockable: All Luigi Ghosts

To unlock all the Luigi Ghosts at once, collect 9,999 coins.
Gus
Hint: Cloud Mario Cataclysm

In the Shiverburn Galaxy, get really close to a Cloud Flower and let yourself get singed by a fiery projectile. Quickly grab the Cloud Flower. You should see that the three clouds follow Mario but we will not be in his Cloud Form.
fleish
Hint: Spin Kick

Crouch by holding down the Z button on the nunchuk and shake the Wii Remote to spin to do a Spin Kick. You can crouch to avoid Boomerang Bros. and crouch-walk up to them to kick them. Jump again to perform a second spin immediately with little pause between the two.
fleish
Hint: Super Secret Dive

Mario’s move list is seemingly endless — even expert players may not be aware of this one. To perform the awesome flipping high dive, you need to find a place high above deep water. Try Starshine Beach — run up the small sandy incline at the start of the level and look for a wooden plank hanging off of one side. Walk to the edge and Mario should look down at the water. Turn around while standing in this spot and perform a back flip by holding Z on the nunchuk and pressing JUMP. Mario will then perform this obscure move.

Addition by Rory: While on the wooden plank in Starshine Beach Galaxy or on the ledge with the 1-Up mushroom in the Slimy Spring Galaxy, run until you are at the edge, stop and then jump in one, FLUID motion. Mario will perform a front flip and then dive.
Orion
Hint: Infinite Starbits

Go to Chompworks galaxy and pick the first Star. Go to the second planet. You know that Chomp that runs into the robot? He produces starbits! If he stops, just enter and exit the pipe.
Harrison Savage
Unlockable: Rosalina Icon

After completeing the game by with all 242 Stars, Rosalina will appear as a game icon on the title menu.
Greg
Cheat: Save Your 1-Ups

You usually start the game with 5 lives, even if you save the game. You can use the “Mysterious Letter” to save all of your 1-Ups between gaming sessions — it’s slower than just racking up a bunch of lives using the turtle method each time you begin a game, but here it is anyway: If you start a different save file (you can simply copy your file over), it will automatically pass on all of the lives you had in the other file through Mailtoad. Save and quit, then return to the file you want to play and the lives are passed back again. Note: If you go into the same save file twice in a row you’ll get the 5-Up Princess Peach letter instead.
bkid
Cheat: Infinite (Very Slow) 1-Ups on Starship Mario

Collect some 1-Ups on the ship with either Mario or Luigi. Switch to the opposite character, and the 1-Ups will be back! Switch back, and they will still be there!
Dustin
Hint: Duck the Boomerangs

When you’re facing the Boomerang Bros. you can crouch (press Z on the nunchuk) to avoid the boomerangs. Walk over to the Bros. while crouching and spin to kill them.
Swiftphantom
Easter Egg: Death in the Credits

Grab a Bee Mushroom as the credits roll and wait for the Shiverburn / winter area. When the page flips, fly toward the screen before you land in the snow or even come in view. You should fall to your death. The screen will be black, and you’ll hear sound effects from the credits. At the end, it says “THE END” with “TOO BAD” in the background.
Unlockable: Banker Toad Gear

Deposit star bits to change the Banker Toad’s gear.

* Scuba Suit – 6000 star bits
* Explorer Outfit – 8000 star bits
* Glasses – 1000 star bits
* Pickaxe – 4000 star bits
* Spear and shield – 2000 star bits

Weegy
Unlockable: Death Count

Beat The Perfect Run (the Comet for The Grandmaster Galaxy) to unlock a death count for your game on your save profile. This number appears in the upper right above your Star count. It’s probably pretty high.
gravytrain
Cheat: Infinite Lives

This fantastic cheat will get you 99 lives easily — you can always return for more! Go to the Supermassive Galaxy in World 4 and choose the first Star challenge. Play through the level until you get to the hockey puck-shaped planet with three supermassive Koopa turtles patrolling it. DO NOT grab the Spin Drill — you’ll have to get hit to lose it if you do! Run up behind a Koopa and long-jump (press Z while running and then press JUMP) onto its back. You need to long-jump from about a turtle-shell-length behind it to catch the “sweet spot.” Continue to hold the analog stick to the RIGHT and hold JUMP to continually bounce off the Koopa’s shell. If you fall off or hit the head, try again. If you hold these buttons you should be able to maintain momentum while constantly bouncing on the shell. After a few bounces you’ll rack up 1-Ups for each hit.
Sebastian
Hint: Skate Backwards

While on ice, press Z to skate backwards! It looks really cool!
taiwanman0610
Hint: Luigi on Title Screen

Exit the game while playing as Luigi instead of Mario and you’ll see his face on the title screen (as long as you chose Mario’s for your default profile face).
Sebastian
Hint: Super Punt

When you are close to a Hammer Bro., do a long jump and spin. Mario will kick him down, then finish him of with another kick.
IGN Guides
Unlockable: Grandmaster Galaxy Comet, “The Perfect Run”

Near the level list signpost on the main platform of Starship Mario is a Toad Banker who will store your star bits so other save profiles can use them. If you deposit 9999 star bits into the Toad Bank and you’ll unlock the Grandmaster Galaxy (Daredevil) Comet, “The Perfect Run”. You will NOT be notified or shown the Comet arriving at the galaxy. Just go there and play it!
IGN Guides
Cheat: Yoshi’s Infinite Flutter Jump

This tricky move, when perfected, can allow you to reach untold heights and explore off-limits areas. Jump and hold A to “flutter.” As Yoshi flutters, TAP Z while still holding A and then release A quickly. Press A again to flutter jump again in MID AIR. The goal is to get Mario to duck, NOT dismount, then quickly flutter again. Try to catch Yoshi at the height of each flutter to perform this maneuver.
IGN Guides
Unlockable: Profile Crowns

Perform the following actions to win the image of a crown next to your save profile.

* Silver Crown – Get 120 Stars
* Gold Crown – Get 240 Stars
* Platinum/Jewel Crown – Get 242 Stars and become the “Master of Galaxies.” This title will appear next to your crown.

IGN Guides
Unlockable: Alternate Ending

Collect 120 Stars to see an alternate ending cutscene with Rosalina reading to Lumas and discussing Green Stars.
IGN Guides
Unlockable: Grandmaster Galaxy

Collect 240 Stars (120 Gold + 120 Green) to unlock the Grandmaster Galaxy in World S. This 2D level will test your Yoshi tongue-slinging skills. It has a Comet Medal and a two stars to collect, pushing your star count to a whopping 242 Stars!
IGN Guides
Unlockable: World S

Beat World 6 and you’ll view the game’s ending … but it’s not over yet! You’ll unlock an entire new world, World S, as well.
Snarfadarf
Hint: Co-Op Sound Effects

In co-op mode, player 2 can press any button to make wacky sound effects! UP, DOWN, LEFT, AND RIGHT will make sound effects on the 1st player’s Wii-Mote while -, +, 1, and 2 will make sound effects on the 2nd player’s.
IGN Guides
Unlockable: Luigi

Get 30 Stars to unlock Luigi for play on certain levels. You can talk to Luigi at the start of a level to control him. Beat the level and you’ll unlock a time trial “ghost.”

If you beat the game, a door will open on Spaceship Mario’s forehead, right under the main platform. Enter this door to transform into Luigi and play any level as the clumsier bro.
IGN Guides
Unlockable: Staff Ghosts

Beat a level using Luigi to unlock a “ghost” recorded by the game’s developers. You can try and beat this ghost as it makes its way through the level at mach speed!
IGN Guides
Unlockable: Green Stars

Beat the game after you get the 120 Stars and you’ll unlock 120 more Green Stars to collect! Green Stars are stars located at tough-to-reach locations in the previous galaxies. They have NOTHING to do with Luigi.
IGN Guides
Hint: 1-Up Mushrooms on Spaceship Mario

You can collect several 1-Up Mushrooms on Spaceship Mario. As you collect stars, the following 1-Up options will appear on Spaceship Mario.

* Grab Yoshi off of the “nose” and use the star pegs to swing up to a hidden island with 10 fruit. Eat them all for a 1-Up.
* Grab a Cloud Flower and make platforms to reach a 1-Up on a cloud high above.
* Spin into the random item block for a chance at a 1-Up.
* Near Mario’s left ear (your right) is a warp pipe that takes you to a 1-Up minigame. Feed the Luma to spin a number of random item blocks for a chance to win 1-Ups.
* Talk to the Gearmo Robots when they show up on the planet to receive 1-Ups.

IGN Guides
Hint: Super Ground Pound

Jump, shake the Wii-Remote to spin and QUICKLY press Z to perform a super ground pound. This move will allow you to hone-in on enemies below you; a heat-seeking butt-stomp, if you will.

Oh and if you have any other cheats you want to share, tricks too, just put them in a comment and I will add them to the list.