Megaman
Weapon trick:
Whenever you use a weapon like the Elec Beam, press select to score an extra hit. This will only work in the original version. It will not work on the Wily Wars

Megaman 2
All weapons and items and four energy tanks:
A5, B2, B4, C1, C3, C5, D4, D5, E2
Dr. Wily's Castle:
A1, B2, B4, C1, C4, D1, D3, E3, E5
Have 4 energy tanks in the beginning:
A5, B1, B3, C4, D2, D3, E1, E4, E5

Megaman 3
All weapons, All items, 9 energy tanks, no bosses:
Blue: A3, B5, D3, F4- Red: A6

Megaman 4
Dr. Cossack's Castle, all weapons and all items:
A1, A4, B5, E2, F1, F3

Megaman 5
Go to Protoman's Stage:
Red: C1, D4, F6 Blue: B4, D6, F1

Megaman 6
All weapons and all Items:
B6, D4, F2, F4, F6

Megaman 7
To get to Wily's castle with everything:
(left to right) 1415, 5585, 7823, 6251
Versus mode (Megaman vs. Bass)
Enter the same code above, hold the L and R buttons on the controller, then press start.

Megaman X
All bosses defeated:
(left to right) 8441, 2136, 4421
All the goodies:
(left to right) 4131, 6712, 1221
Start game with all items:
(left to right) 2653, 3858, 7584
Hadouken:
First, complete all stages and all weapons. Just visit Armor armadillo's stage 5 times and the Hadouken is yours

Megaman X2
All Weapons and Items:
6474, 6347, 6828, 7223
Shoryuken:
Get everything maxed out (life, energy, subtanks etc.) then when you reach Agile's stage, there will be a two-way course. Pick the one on top by crystallizing the bat and using the stairs.

Megaman X3
Everything except the Gold Armor, has Zero alive:
(left to right) 4474, 2365, 6162, 7188
Zero's light sabre:
To get it by yourself, use Zero when you're battling the mosquito or you can just use the password (left to right) 1454, 3535, 6162, 7162