DD61-6D0D Start with 1 life--Normal/Hard only
DF61-6D0D Start with 2 lives--Normal/Hard only
D061-6D0D Start with 5 lives--Normal/Hard only
DB61-6D0D Start with 10 lives--Normal/Hard only
F661-6D0D Start with 25 lives--Normal/Hard only
7F61-6D0D Start with 50 lives--Normal/Hard only
1461-6D0D Start with 99 lives--Normal/Hard only
C22D-ADDF Infinite lives
DF6F-6DDD Start with 1 continue--Easy/Normal only
D46F-6DDD Start with 2 continues--Easy/Normal only
D96F-6DDD Start with 5 continues--Easy/Normal only

With the continue codes, if you have over 10 continues, it 
doesn't show
DC6F-6DDD Start with 10 continues--Easy/Normal only
FB6F-6DDD Start with 25 continues--Easy/Normal only
746F-6DDD Start with 50 continues--Easy/Normal only
176F-6DDD Start with 99 continues--Easy/Normal only
C266-DD6F Infinite continues
D083-6D0D + BA83-67DD Start with all weapons at maximum power (4 power-ups) 
6D22-640F + F122-646F Don't decrease weapon power after dying
DF83-6D0D Start with blue weapon
D483-6D0D Start with yellow weapon
4A82-AF0D Never change weapon type
C22D-0404 Infinite wheel time
C226-DDD4 Invincibility (falling in a hole still kills you)
6D28-ADDF Level timer doesn't count down (infinite time)
DD8E-6DDD Start with no "smart lines"
DF8E-6DDD Start with 1 "smart line"
D48E-6DDD Start with 2 "smart lines"
D08E-6DDD Start with 4 "smart lines"--only 3 shown at once
D98E-6DDD Start with 5 "smart lines"--only 3 shown at once
DC8E-6DDD Start with 10 "smart lines"--only 3 shown at once
FB8E-6DDD Start with 25 "smart lines"--only 3 shown at once
748E-6DDD Start with 50 "smart lines"--only 3 shown at once
178E-6DDD Start with 99 "smart lines"--only 3 shown at once
C226-D704 Infinite "smart lines"
D46D-64DD Start on level 2
D76D-64DD Start on level 3
D06D-64DD Start on level 4
D96D-64DD Start on level 5
D16D-64DD Start on level 6
D56D-64DD Start on level 7
D66D-64DD Start on level 8
DB6D-64DD Start on level 9
DC6D-64DD Start on level 10
D86D-64DD Start on level 11
DA6D-64DD Start on level 12