Here's a 15 minute video of Oni and Evil Ryu in action. The video quality is great, but the camera man is either very frail or very drunk, as he keeps fumbling and flopping around with the camera. The two guys playing also seem a bit off, as they have the tendency to just suddenly stop fighting every once in a while. Be prepared to be occasionally annoyed. There are four shorter, slightly blurry videos below, but what the lack in length and fidelity, they make up for in action. The Dee Jay Vs. Oni vid is particularly awesome.
A quick note to people complaining about these characters -- stop being bratty. I would have preferred for Capcom to give us Elena, Poison, Rolento or all new characters as well, but considering that Evil Ryu and Oni are meant to be unplayable bosses (only accessible for play through messing with the debug screen) it's hard to argue that Capcom has "done us wrong". Evil Ryu and "nameless" Akuma, are the two original "super bosses" of the Street Fighter series, and the appearance of Oni and Evil "hole in his chest" Ryu in Super Street Fighter 4: Arcade Edition is a great way to carry on their legacy. When it comes to intimidation factor, ties to the Street Fighter storyline, and pure gravitas, no other Street Fighter characters can compete with these two (except maybe Gouken, and Capcom has already played that card).
OK, I'll get off my high horse now. I hope you enjoy these videos. I'm sure there will be more popping up throughout the day, so check back to this post for potential updates.