Gold/Silver:

Genes:
Attack/Defence: 01XX3FDA
Speed/Special: 01XX40DA

For max stats, put in FF instead of the XX. Have the Pokémon in the first slot, then on then off the gameshark, then place it in Bill's PC. Withdraw it, then you have perfect stats.

Hidden Power IV's:
Dark - FFFF
Dragon - FEFF
Ice - FDFF
Psychic - FCFF
Electric - EFFF
Grass - EEFF
Water - EDFF
Fire - ECFF
Steel - DFFF
Ghost - DEFF
Bug - DDFF
Rock - DCFF
Ground - CFFF
Poison - CEFF
Flying - CDFF
Fighting - CCFF

Put in those values for the Gene codes above.

Fight shiny Pokémon:
010719D1

Enemy always asleep and burned:
01FFFDD0

Infinite money:
019973d5
019974d5
019975d5

Change Gender (1st position):
Male:
01FF3FDA
01FF40DA

Female:
O11F3FDA
01FF40DA

Change Character's icon:
01XXFFD1

00 = You
0C = Main
18 = Second Main
24 = Third Main
3C = Fourth Main
48 = Fifth Main
54 = Sixth Main

This code is confusing. Your icon will change where you are. If you are in a Gym with the Main code on, you will be the leader. If you have Second Main on, then you are one of the trainers. Etc. If you are outside then you are a Random person. In areas with not many people (caves etc), the higher Main numbers may not work properly.

All Johto badges:
01ff7cd5

All Kanto badges:
01ff7dd5

Speed up egg hatching (first slot):
010145DA

Happiness Modifier:
01XX45DA
00: Your pokemon hates you
46: Where you start from after catching or trading.
DA: The requirement for happiness evolution. FF: The maximum.

Have all of the room decorations:
01FF0BD8
01FF0CD8
01FF0DD8
01FF0ED8
01FF0FD8
01FF10D8
010311D8

No Random Battles:
01000bd2

Catch a Trainer's Pokémon:
010116D1

Go into battle, and when the Pokémon you want is sent out, pulse the Shark, and proceed.

Fight a certain gender:
Female: 010419D1 Male: 010519D1

Cystal:

Infinite Money
910f4ed8
91424fd8
913f50d8

Have All Badges
91ff57d8
91ff58d8

Fight a Shiney Pokemon
910730D2

Fight a certain Gender
Female: 910430D2
Male: 910530D2

Happiness Modifier (Fist Position):
91XXFADC
00: Your Pokemon hates you
46: Where you start from after you catch or trade
DA: The requirement for happiness evolution
FF: Maximum

Have all badges:
91FF57D8
91FF58D8

Steal Trainers Pokemon:
91012DD2: