Sonic the Hedgehog

These are from the Game Genie Code Book
(Special thanks to Psycoke for helping me test them):

ATBT-AA32         MASTER CODE--must be entered!
AE3T-AACL     Start with 1 life
AY3T-AACL     Start with 5 lives
AE0T-CABE     Once invincible, Sonic stays invincible
SCRA-BJX0      Each ring counts as 2 rings
SCRA-BNX0     Each ring counts as 3 rings
SCRA-BTX0      Each ring counts as 4 rings
SCRA-BYX0     Each ring counts as 5 rings
SCRA-B2X0      Each ring counts as 6 rings
SCRA-B6X0      Each ring counts as 7 rings
SCRA-BAX0     Each ring counts as 8 rings
GJ6A-CA7A      Infinite lives
AJ3A-AA46      Level Select menu
AY3T-BA4R     Start with 5 Chaos Emeralds

Sonic 3

ACGA-AA8T Only 1 blue sphere needed for a Chaos Emerald
SCFT-B2T4 Only 2 Chaos Emeralds needed to become Super Sonic
 

Sonic Spinball

AFBT-5N7G Start on level 2
AKBT-5N7G Start on level 3
APBT-5N7G Start on level 4 (Showdown)
AXBA-4A4T Infinite lives

 
Sonic Chaos (Game Gear)

008-3BD-E6E Infinite time
0A2-1EC-E6E Each ring is worth 10
996-93C-E66 Sonic starts with 99 lives
506-99C-F7E Tails starts with 50 lives

Sonic & Knuckles
Special Thanks to Stephen T. Stone for sending these.

Sonic & Knuckes, without a cartridge attached:
AFKT-AAG0            Start with 1 life
AKKT-AAG0           Start with 2 lives
AVKT-AAG0            Start with 4 lives
AZKT-AAG0            Start with 5 lives
A7KT-AAG0            Start with 7 lives
BFKT-AAG0            Start with 9 lives
DFKT-AAG0            Start w/25 lives
GKKT-AAG0           Start w/50 lives
NPKT-AAG0            Start w/99 lives

With Sonic 3 attached:
AWXT-CA4C    Don't loose rings when hit
HXRT-AA6A     Infinite time
ATGT-CA3Y      Speedy shoes don't run out w/time
RENT-C6V6       Sonic always uses fireball Spin Dash
RENT-C6YA      Sonic always double jumps
RGSA-A6YY    Only one blue sphere needed to gain Emerald
AANA-CNA0    Sonic jumps as high as Knuckles
4ANA-CRA0     High Jump for Sonic
2ANA-CWA0    Super Jump for Sonic
AANA-C4A0     Mega Jump for Sonic
AANA-DYA0    Hyper Jump for Sonic
TB5T-CNCR    Knuckles jumps as high as Sonic
PV5T-CRCR     High Jump for Knuckles
AB5T-CWCR    Super Jump for Knuckles
AB5T-C2CR     Mega Jump for Knuckles
AB5T-DTCR        Hyper Jump for Knuckles
ALNA-AACR      Rings in Special Stage worth 2
ARNA-AACR    Rings in Special Stage worth 3
AWNA-AACR    Rings in Special Stage worth 4
A0NA-AACR    Rings in Special Stage worth 5
BLNA-AACR    Rings in Special Stage worth 10
A2NT-CAG6    6 Emeralds needed for Super Sonic
AYNT-CAG6    5 Emeralds needed for Super Sonic
ATNT-CAG6    4 Emeralds needed for Super Sonic
ANNT-CAG6    3 Emeralds needed for Super Sonic
AJNT-CAG6     2 Emeralds needed for Super Sonic
AENT-CAG6     1 Emeralds needed for Super Sonic
AANT-CAG6     No Emeralds needed for Super Sonic
AANT-CAGY + AAPA-CAB8    No Emeralds needed for Hyper Sonic
NTNT-CAHL    100 rings needed for Super/Hyper Sonic
FANT-CAHL    40 rings needed for Super/Hyper Sonic
DENT-CAHL    25 rings needed for Super/Hyper Sonic
BJNT-CAHL     10 rings needed for Super/Hyper Sonic
AENT-CAHL    1 ring  needed for Super/Hyper Sonic
A36A-CACW    6 Emeralds needed for Super Knuckles
AZ6A-CACW    5 Emeralds needed for Super Knuckles
AV6A-CACW    4 Emeralds needed for Super Knuckles
AP6A-CACW    3 Emeralds needed for Super Knuckles
AK6A-CACW    2 Emeralds needed for Super Knuckles
AF6A-CACW    1 Emerald needed for Super Knuckles
AB6A-CACW    No Emeralds needed for Super Knuckles
AB6A-CACL + AB6A-CAHR No Emeralds needed for Hyper Knuckles
NV6A-CADA     100 rings needed for Super/Hyper Knuckles
FB6A-CADA      40 rings needed for Super/Hyper Knuckles
DF6A-CADA      25 rings needed for Super/Hyper Knuckles
BK6A-CADA     10 rings needed for Super/Hyper Knuckles
AF6A-CADA      1 ring needed for Super/Hyper Knuckles
NTPT-CA50        Rings not used up as Super/Hyper Sonic/Knuckles
RHJA-E60L         Bonus round after every checkpoint
BXLA-EA5G        Bonus round always Slot Machine
A5LA- EA5G        Bonus round always Glowing Spheres
ACCT-CA2R        Never drown
AKVT-AA76 + AMNA-EA24    Keep rings between levels
96BA-CAG6 + 98MA-CAFO     Keep shields when hit

With Sonic 2 attached
AX6D-AA3W        Don't lose rings when hit
HWLX-GA2Y        Infinite time
SD5X-BJT2            Rings worth 2
SD5X-BNT2           Rings worth 3
SD5X-BTT2            Rings worth 4
SD5X-BYT2            Rings worth 5
SD5X-B2T2            Rings worth 6
SD5X-B6T2            Rings worth 7
SD5X-BAT2            Rings worth 8
AE5X-AAFY            Start w/1 life
AY5X-AAFY            Start w/ 5 lives
A65X-AAFY            Start w/7 lives
BE5X-AAFY            Start w/9 lives
DE5X-AAFY            Start w/25 lives
GJ5X-AAFY            Start w/50 lives
KN5X-AAFY            Start w/75 lives
NN5X-AAFY            Start w/99 lives
JV1D-CA6W            Infinite lives
PVWD-CRDC           High Jump
ABWD-CWDC        Super Jump
ASWD-C2DC            Mega Jump
ABWD-DTDC            Hyper Jump