Here’s a list of things you can punish with spd, which has a 2-frame startup. I’m not putting any far attacks, which you don’t have the range to punish, but I am putting crouching attacks and close specials like point-blank fireballs because you can punish them if you’re close enough. I’m also not listing specials, supers, and ultras where it’s obvious that you can punish them, but I am listing them where it’s not obvious (like with Ken’s hurricane kicks or Sim’s super). Anyway:
Ryu: close standing strong, close standing fierce, close standing roundhouse, crouching fierce, crouching roundhouse, short hurricane, fireball
Ken: close standing strong, close standing fierce, close standing roundhouse, crouching fierce, crouching forward, crouching roundhouse, overhead kicks, fireball (on hit as well), all hurricane kicks
Chun: close standing strong, close standing fierce, close standing forward, close standing roundhouse, crouching strong, crouching roundhouse, back+forward kick launcher and follow-up, down-forward+short, fireball, roundhouse and ex spinning bird
Honda: overhead stomp, roundhouse and ex buttslam
Blanka: close standing fierce, close standing roundhouse, crouching strong, crouching fierce (on hit), crouching roundhouse
Zangief: close standing fierce, close standing forward, close standing roundhouse, crouching strong, crouching forward, crouching roundhouse, down-toward+roundhouse, lariat, all green hands (on hit, except ex)
Guile: close standing strong, close standing forward, close standing roundhouse, crouching fierce, crouching forward, crouching roundhouse, overhead, knee bazooka (back/toward+short), sobat kick (back/toward+forward)
Dhalsim: back+strong, down-toward+all punches, all slides, down-back+roundhouse, yoga fire, jab yoga flame, super
Boxer: close standing fierce, close standing forward, crouching fierce, crouching roundhouse, all regular rush punches, all regular rush uppers, all low rushes, all overhead rushes, all regular down-toward kick rushes, all headbutts, all levels of tap except level 1
Claw: close standing roundhouse, crouching strong, crouching fierce (on hit), crouching roundhouse, down-toward+forward, wall dive
Sagat: close standing roundhouse, crouching forward, crouching roundhouse, overhead, all low tiger shots, tiger knee that does two hits
Dictator: crouching fierce, crouching roundhouse, all psycho crushers, all scissors except short
Viper: crouching short, crouching forward, crouching roundhouse, ex thunder knuckle, regular seismos
Abel: close standing jab, close standing fierce, close standing forward, close standing roundhouse, crouching fierce, crouching forward, crouching roundhouse, all changes of direction, all change of direction follow-ups
Fuerte: target combo
Rufus: close standing fierce, close standing roundhouse, crouching forward, crouching roundhouse, toward+forward overhead, toward+fiece, jesus kick, jesus kick overhead follow-up
Akuma: close standing fierce, close standing roundhouse, crouching fierce, crouching roundhouse, toward+strong overhead, all hurricane kicks