use twds + fierce, SSB, neutral throw, s. roundhouse. all of them have pretty good stun value. when you use the neutral throw, make sure you mash it like crazy.
as far as which combos stun the most, DooM mentioned the biggest stunner. another one is (without the jump-in):
s. roundhouse x EX MGB -> twds + forward x fierce Jet Uppercut
without a jump-in, his best one is probably
s. roundhouse x EX MGB -> EX Jet Uppercut -> fierce Jet Uppercut
that has other variations, but it’s also pretty difficult to land. if you’ve got it down good, then go for it. i don’t usually use it.
honestly though, even if Dudley has pretty good stunning capability, i don’t think he’s quite up there with Makoto, SA3 Ryu or Necro. it’s not really his game plan to dizzy someone. if it happens, then it’s a bonus, but i find that if my goal is to stun my opponent, i get sidetracked. i personally find that going for the 50/50 set-ups is more the way to go. again, the dizzying is just a bonus to that if it happens.