Bioware has confirmed that every party member from the first game will appear in ME2 in
some capacity, provided they survived your playthrough of course. Tali is, as far as I know, the only one who's actually been confirmed as being in the ME2 squad so far.
Gametrailers TV had a
Mass Effect 2-centric episode that premiered last night, gave (very brief) reveals of both the Illusive Man character (who, if my
internet sources are correct, is voiced by Martin Sheen) and the Salarian party member. It also looks like they're giving classes more unique abilities. They specifically talk about the Vanguard in the GTTV episode, which has a new biotic charge ability which basically looks like a short-range teleport/ramming ability that allows them to get up close and stun one enemy, which you can then shotgun in the face from close range. If you put enough points into the ability, you get a bullet time effect after the charge too. Looks pretty neat, I'm curious to see the spins they put on all the other classes too.
Also, I'm really impressed by how slimmed-down and slick-looking the HUD is this time around. It takes up much less of the screen and complements the new closer camera angle well.