Feel free to correct me, other players, but here's what I remember (typed all at once, so sorry for spelling mistakes):
WARNING: SPOILERS
CRISTAL
Get all 7 to kill all the enemies and gain an extra life. If you collect them in order (C-R-I-S-T-A-L) you will also gain 150,000 points. Each letter is worth 5 points.

GOLDEN SHIELD
Gives Igor a barrier for roughly 10 seconds. This barrier will protect against everything except for the fireball.

SILVER SHIELD
Gives Igor a barrier for the rest of the level.

BEACH BALL
A beach ball bounces across the screen. All enemies that touch it will be stunned.

MAGIC LAMP
Lets you have one more bomb onscreen at any given moment.

BLACK MAGIC LAMP
Lets you have unlimited (?) bombs onscreen at any given moment.

YING-YANG
Freezes all enemies; ice lasts for much longer thatn your regular bombs do.

SNEAKERS
Lets you run at double speed.

STAR
2 Bubbles appear and bounce around the screen. Any enemy that touches them will be stunned.

BAD EYE
A 10Ton weight falls from random places on the ceiling. This weight kills everything it touches, including Igor.

PHONE
Once you collect 5, adds a 25% bonus to whatever snowflakes you buy.

UMBRELLA
Lets you skip the current level.

BLUE UMBRELLA
Lets you skip he current level and the one after it.

BIKER HELMET
Your kicks are more powerful, sending bombs farther.

BLUE SPOT SHROOM
Every time one of your bombs explodes, a blue mushroom appears.

DAFFODIL
Makes you fall much slower.

SUNFLOWER
Kills all enemies onscreen, giving you the large crystal if you havent killed anything yet.

TREASURE CHEST
Makes 5 random crystals appear.

RADIO
Kills one random enemy.

BOOT
Causes Igor to run much slower. The opposite of the Sneaker.

CRYSTAL BALL
Shoots iceballs at all enemies onscreen; if they hit, the enemy is frozen.

ICE METEOR
Causes a Ice Meteor to fall from the top-right corner to the bottom-left; any enemy that touches it is frozen.

SILVER METEOR
Causes fireballs to rise from the bottom and fall from the top; if they touch an enemy, they turn into Crystals.

LIGHTBULB
After collecting 10 of them, the lower levels lose almost all their darkness.

LILYPAD
Any CRISTAL letters you collect will now be worth 30 points instead of 5.

TROPHY
All enemies onscreen are stunned.

DIAMOND RING
Lets Igor shoot a fireball ahead of him instead of bombs.

BLUE GLASSES
Flips the screen and your controls left-right. Left is now Right, and vice-versa.

RED GLASSES
Flips the screen up-down. Up is now Down, and vice-versa.

ACE OF SPADES
Turns all enemies into blue crystals.

ACE OF CLUBS
Turns all enemies into red crystals.

GOLDEN IGOR
Gives Igor an extra life. Also, after collecting 5 of them, you gain an extra life at the beginning of every game.

FROST NECKLACE
Lets Igor shoot an Iceball ahead of him instead of bombs.

TOTEM POLE
Arrows fly across the screen; all enemies that hit them will die.

EASTER ISLAND HEAD
Whenever you hit the ground, all enemies are stunned for a very short time.

CONSTELLATION

STATUES
Colecting all 12 will give you 2 bombs at the start of every game. They also make Red Line Stars appear.

CONSTEALLATION

POTIONS
Collecting all 12 will give you the permanent ability to kick bombs up by pressing the Down button.

RAINBOW
Makes 7 random CRISTAL letters appear.

RUBBER DUCKY RING
Gives you 2,500 points for every enemy onscreen and 600 points for every spike/razor.

CACTUS
Gives you 10 points everytime you jump.

ARROW RING
Lets Igor shoot an arrow ahead of him instead of bombs. The 1st enemy the arrow hits will die.

CANDLE
Collecting 10 will make the lower levels a little brighter.

TURTLE
Causes the enemies to move a bit slower.

FOUR-LEAF CLOVER
Gives you 10 points everytime you kick a bomb.

DRAGONHEAD
Shoots 2 fireballs horizontally.

WIZARD HAT
Turns all enemies into ordered Crystals. Thus, the 1st enemy turns into a Blue Crystal, then the 2nd turns into a Green Crystal, the 3rd turns Red, 4th Yellow, and so on.

LEAF
Gives you 10 points for every few feet you walk.

ORANGE GLOB
Causes a bunch of Purple Striped Candies to fall from the sky.

BLUE GLOB
Causes a bunch of Blue Striped Candies to fall from the sky.

GREEN GLOB
Causes a bunch of Cherry Candies to fall from the sky.

BLUE FISH
When you finish the level, a bunch of Blue crystals will fall from the sky.

RED FISH
When you finish the level, a bunch of Red crystals will fall from the sky.

YELLOW FISH
When you finish the level, a bunch of Yellow Crystals will fall from the sky.

SNAIL
Causes the enemies to move very slowly.

BLUE POLISHED STONE
All enemies and spikes disappear, and Silver Crystal Shards appear on all platforms. If you collect them all, you get 50,000 points!

GOLDENEYE PYRAMID
Kills the next enemy in the Order of the Great Crystal.

SILVER ARMORPLATE
Firballs rain down on the enemies.

HAMMER
Any enemies directly in front of Igor will die.

MAGGOT
Causes a random enemy to turn into a maggot. The last enemy turns into a Diamond.

SOCK PUPPET
Causes Igor to shrink, greatly decreasing his jumping ability.

DRAGON EGG
Causes a random enemy to turn into a 50,000-point Dragonfly.

BANANAS
Everytime Igor jumps down from a platform, he will slip and remain stunned for a moment.

STRAWHAT
Prohibits ou from using bombs for roughly 30 seconds.

MAILBOX
Makes all enemies dissappear, and drops several Packages from the sky.

LORD'S RING
Causes 2 point items to appear in every level until you die.

PACKAGE
Contains either 5,000 points or a Pear Bomb.

CARROT
Appears on Level 103. Worth 100,000 points. Appears beside your name in the forums, and also ive you an extra life at the start of every game.

RED HEART
Gives you an extra life at the start of every game.

GOLD HEART
Gives you an extra life at the start of every game.

ICE HEART
Gives you an extra life at the start of every game.

SNOWFLAKE
Gives you 5 games.

ICE SPIKE
After collecting 2 of them, you get 10 games.

HAVENT A CLUE
After collecting 2 of them, you get 20 games.

CROWBAR
Appears on Level 3.1. Opens up the keyhole in 3.1. Worth 10,000 points.

CRYSTALS
Worth varying amounts of points.
Blue - 500 points
Green - 2,000 points
Red - 4,500 points
Yellow - 8,000 points
Purple - 12,500 points
Orange - 18,000 points
Black - 24,500 points
Also, if you kill the enemies in the right order, a large Crystal falls from the sky. The color depends on tge amount of enemies in the level.
Large Green - 10,000 points
Larde Red - 22,500 Points
Large Yellow - 40,000 Points
Large Purple - 64,500 Points (?)
Large Orange - 90,000 Points
Large Black - ?????
Large Ruby - ?????
Large Jade - ?????
Large Moon Jewel - ?????

HAMBURGER
Worth 1,000 points.

PURPLE STRIPED CANDY
Worth 500 points.

BLUE STRIPED CANDY
Worth 1,000 points.

CHERRY CANDY
Worth 2,500 points.

BLUE LOLLIPOP
Worth 5,000 points.

GREEN LOLLIPOP
Worth 15,000 points.

DIAMOND
Worth 2,000 points.

RUBY
Worth 5,000 points.

JADE
Worth 15,000 points.

MOON JEWEL
Worth 25,000 points.

SMALL CAKE
Worth 800 points.

NUFFIN
Worth 300 points.

LARGE CAKE
Worth 1,000 points (?).

WEDDING CAKE
Worth 12,000 points.

CAKE SLICE
Worth 1,200 points. (?)

CRYSTAL SHARDS
Worth varying amounts of points. These appear on all platforms whenever you colect a Polished Stone.
Silver - 75
Orange - 1,200
Green - ?????
Purple - 10,000

ICE CREAM
Worth 1,800 points. (?)

SUNDAE
Worth 3,500 points.

CHICKEN
Worth 10 points.

JAR OF RED
Worth 10,000 points.

TAFFY
Worth 5,000 points.

JAR OF BLUE
Worth 20,000 points.

EGG
Worth 500 points.

POTATO
Worth 1,500 points. (?)

LICORICE
Worth 600 points.

COOKED EGG
Worth 1,000 points.

PINK WHITEBOARD ERASER
Worth 8,000 points

LOLLIPOP
Worth 750 points. (?)

POPSICLE
Worth 800 points. (?)

CHOCOLATE CASHEW
Worth 3,000 points

BLUE SHROOM
Worth 5 points.

RED SHROOM
Worth 10 points.

COIN
Worth 2,500 points. Found mainly on Lv. 16.1, but can also be found in... certain spots.

SILVER COIN
Worth 5,000 points.

GOLD COIN
Worth 25,000 points.

COKE
Worth 1,200 points.

FRIES
Worth 1,000 points (?).

PIZZA
Worth 1,800 points.

PEANUT
Worth 50 points.

GUMMY GHOST
Worth 800 points.

COOKIE
Worth 1,300 points (?).

BROWN LOAF
Worth 3,000 points (?).

SEED
Worth 5 points.

BEANS
Worth 800 points.

SLINGSHOT
Worth 1,800 points (?).

BEER
Worth 900 points.

CHESTNUT
Worth 3,000 points.

CAN O' SAUSAGE
Worth 575 points.

CAN O' BEANS
Worth 800 points (?).

CAN O' BERRIES
Worth ??? points. (I dont remember

)

GREEN CAN
Worth 175 points. (?)

PURPLE CAN
Worth 300 points. (?)

GARLIC TOAST
Worth 1,200 points.

CHOCOLATE CAKE SLICE
Worth 1,800 points (?).

CRACKER CAKE SLICE
Worth 1,300 points. (?)

DUCK COFFEE
Worth 800 points.

GHOST TOAST
Worth 900 points (?).

PANCAKE
Worth 400 points (?).

NUT
Worth 3,000 points.

CAPLESS ACORN
Worth ??? points.

NOODLES
Worth 650 points.

CHOCOLATE BREAD (

)
Worth 850 points (?).

JAM BREAD
Worth 650 points.

BUTTER BREAD
Worth 700 points (?).

RED LINE STAR
Worth 1,500 points.

LEMON STATUE
Worth 1,000 points. Appears after beating the Lemons at Level 30.

BOMBINO STATUE
Worth 4,000 points. Appears after beating the Bombinos at Level 40.

PEAR STATUE
Worth 9,000 points. (?) Appears after beating the Pears at Level 50.

STRAWBERRY STATUE
Worth 15,000 points. Appears after beating the Strawberries at Level 60.

KIWI STATUE
Worth 18,000 points. Appears after beating the Kiwis at Level 70.

WATERMELON STATUE
Worth 25,000 points. (?) Appears after beating the Watermelons at Level 80.

RIGOROUS DANGER KEY
Worth 10,000 points. Appears at 55.1 after pressing the button. Unlocks the keyhole at Level 51.

AUTHORIZATION PAPER
Worth 10,000 points. Opens up the keyhole at Level 15.12.

BEER CAN
Worth 800 points. (?)

BEER BOTTLE
Worth 1,000 points. (?)

STAMP
Worth 2,000 points.

PAPER
Worth 10 points.

SAND SHOVEL
Worth 800 points. (?) After collecting all 10 each of the 4 Sand Items (Shovel, Bucket, Castle, Crab), you will unlock 2-Player Mode.

SAND BUCKET
Worth 800 points.

SAND CASTLE
Worth 800 points.

SAND CRAB
Worth 800 points.

KATANA
Worth 1,800 points. (?)

SHURIKEN
Worth 400 points (?).

KUNAI
Worth 800 points (?).

GOLD NINJA STAR
Worth 10,000 points. Appears in Ninjutsu Mode when you complete a level. Collecting 100 unlocks Time Attack Mode.
And thats all the items I have! Phew! That took a long time...
