Well, what a coincidence, I was doing some research because of SF4 (and then those old arcade games too), just some time ago.
I found these:
This seemed right for me, yet I could not instantly find where to buy it:
Somehow they didn't like this one:
IGN: Hori Real Arcade Pro. EX Review
These cost a bit, maybe a bit too much (165$-250$), it looks like a professional choice and they say these are custom made:
IGN: Arcade in a Box Xbox 360 Arcade Stick
The XBOX 360 D-pad is horrible even when playing Oblivion, so I decided if I go for SF4 I should pick up a new controller and maybe that could be great with some other old arcade games too. Well, time will tell what happens, the Mad Catz Fightpad should cost like 40$, and it's not too much
I saw some people complainind the Fightpad D-pad needs more pressure on diagonal than horiz./vert., but is better compared to the 360 original controller D-pad. Well, I actually don't know what are all the games supported with these products, should search later for that info.