Super Metroid Game Genie codes by Grime of www.metroidconstruction.com.
I don't care if you post this on your site or distribute it. I'll add more codes eventually.

44E4-C909
Prevents Samus from losing speed by turning left/right during a spinning jump.

3CC8-456F
Allows space jumping by simply holding the jump button. Space jump also falls a bit slower in the air, and much slower in water.

3CCB-40AF
3CCB-49DF
3CCB-490F
Space jumping can be done faster and at any time, even after falling long distances.

3C81-11D4
3C81-1104
Slows down the acceleration of all beam shots.

3C87-C064
3C87-C0A4
Slows down the acceleration of all charged beam shots.

3C8A-10AD
Slows down the acceleration of all beam shots AND charged beam shots.

B3CB-3967
B3CC-30D7
Missiles move very slowly, almost like torpedos. Doesn't affect super missiles.

DB33-19D1
DC33-15D1
Samus' running speed doesn't reset after landing from a jump.

DB3E-19A1
DC3D-C001
Samus' running speed doesn't reset after landing from a fall.

2D6B-19DF
Renders the speedbooster harmless. Samus only runs faster; no blue echoes, damage to enemies, breaking through speed blocks or super jumping.

D46B-19DF
Blue speedbooster echoes and sound begin earlier than usual (roughly 1 screen's distance).

D06B-19DF
Blue speedbooster echoes and sound begin much earlier than usual (roughly a half screen's distance).

3CE1-C5A9
3CE5-C0D9
3CE5-C009
3CE5-C069
Allows Samus to turn left/right in the air without losing the blue speedbooster echoes, and even walljump if it's done quickly enough.

D1B8-C1A7
D1B3-49A7
Underwater jumps without Gravity suit go very high.

D4B2-C0A7
D7B2-C5A7
Enables walljumping underwater without gravity suit.

D6B2-C007
DCB2-C507
Walljumps go higher.

D5C0-410D
Samus travels much faster through the air after performing a walljump.

3CC0-490F
Space jump works underwater/lava/acid without Gravity suit.

DB8B-31A7
Bombs explode instantly. Use this if you suck at infinite bomb jumping. ;]

D0BE-C907
Bomb jumps go about 4x higher.

D6BE-C907
Bomb jumps go about 8x higher.

FDBE-C907
Bomb jumps go insanely high.

D6BE-C9A7
Bomb jumps underwater without gravity suit go very high.

D6C7-400D
Spring ball travels very quickly through the air when Samus jumps.

D5B6-3107
D5C4-490D
Samus rolls very quickly along the ground in morph ball form.

EE67-4002
1E67-4062
EE67-1102
1E67-1162
Charge beam and its charged shot do insane damage. To give you an idea, Norfair Ridley dies in a single hit.

DF21-1D6C
Speeds up door transitions by eliminating the fade-to-black sequence.