Before I go into the combos I want to let everyone know a universal way on making it a little easier when fighting bison.
1. Focus his single limbs like st hk/mk because he can't cancel them into anything.
2. Neutral jump scissor kicks then land on them and punch similar to balrog's dash punches.
3. After blocking scissors kick you are 0 on guard however since bison's cr lk is really good and has a lot of priority it will more than likely beat out your normal attack may have to do a reversal so its best to back dash away. This will force bison to have to do a unsafe scissors kick to hit you, slide or psycho crusher to chase you which are all of course unsafe.
Oh one more thing before I list the combos. The New Replay channel in SSF4 is really good especially when viewing videos from Asia specifically Japanese videos. Daigo, Mago, Tokido, Sako are all on there and with a lot of unknown japanese players (dunno their tags yet) and they are really showing how to properly play the game. Its perfect especially when you may not have someone who plays a character and you want to see how they work so you check out the vids and pick up a few things.
Alright Akuma u2 char specific combos. There are two ways to hit them either crouching fp or standing close fp.
Close fp combo works on: Dudley, Gouken, Zangief, THawk and Hakan even if they are ducking.
Crouch fp to u2 works on: Sagat, Cammy, Seth, Makoto, Abel, Rufus, Balrog, Cody, Adon, Dahlsim, Ken, Bison, Vega, Deejay, Chun Li
Thats it for now I haven't tested all the characters yet but a few I tested didn't work.