Here's a couple of SF3 videos to show what they are like, although it might be a bit unfair because J is like a legend with Makoto, haha.
Yun
Yang
(oh and you can't really mention J without showing this video)
As for what they're like, well while they're not the same, Rufus was described as being like Yun and Yang has moves in common with Fei Long. They're students of Gen, so they might have moves in common there, but I'm too rusty with them to be able to remember clearly, haha.
As for other SF3 characters, I wouldn't mind SO much if no more were added, since SF3 will come out soon on 360, but if they were, I'd want Elena

Tier lists, well.. hmm.. the best way to describe them is, it's like a spreadsheet, of what would happen if two players with identical skill levels(impossible), played 10 matches, and what the result would be, like 6wins 4 losses if it's good or even 3wins 7 losses if it's a bad matchup, and they total up the numbers, and the ones with the highest amount of points are the highest teirs. Other lists are made from tournament results.
Some may argue that tiers don't matter, which imo is true, at least to a certain extent, and others say you can win with anyone, even so called bad tier characters, like Adon, who was supposed to be terrible, and Rufus, who was supposed to be no.1, and you saw what happened with Justin Wong this year and Gamerbee.
People in general in games are lazy, especially online, so that's why people like that, like tier lists, because they can win with less effort... and you end up with fighting the same small handfull of characters over and over.
info will be posted here, but it's nothing official, plus lots of things were changed from tests previously on other version.
http://www.eventhubs.com/news/2010/sep/10/rumor-ingrid-super-street-fighter-4-arcade/