Obviously, everyone's game could be different. Loyalty, who you sided with during conflicts, and potential deaths could change everything.
Garrus will be back. He's done with the red tape on the Citadel and his squad from Omega is dead. The only reason he MIGHT leave Shepard's squad is because he wants to reapply for Spectre candidacy. I imagine he'll want to stick with Shepard after taking down Saren and then the Collectors to finish the job against the Reapers. Plus he's a fan favorite.
Tali will be back because, regardless of love interest or not, she's grown attached to Shepard, just like Liara did. Same thing as Garrus, too... she may want to stick with him until the end and fight the Reapers. Plus, she's right in the thick of the potential Quarian and Geth war, which could be a big subplot in ME3. She's a fan favorite, too.
I imagine Jacob and Miranda will be back. I know Miranda pledges her loyalty to Shepard during the suicide mission when The Illusive Man's message comes through, asking to keep the base intact. I imagine Jacob says something similar.
If Shepard is Grunt's battlemaster now, he'll probably be back. Since all he wants to do is fight, I can imagine he'll want to stick around after stopping the Collectors in order to get a shot against the Reapers.
Mordin could come back, but I would imagine he'll be a support character because of his age. Either way, not having him in the next game in some form would be a crime since he's awesome.
Thane could come back if he isn't dead from Kepral's Syndrome yet. He may still be out to atone for his sins, but then again, he may want to spend his final days with Kolyat.
I think Jack is gone, but maybe she'll stick around if she wound up being a paragon Shepard's love interest. Otherwise, she's been busted out of prison and has nothing tying her down anymore.
Samara could be different for paragon and renegade Shepards. She mentioned she would come to paragon Shepard's aid if she was called for, but she also mentions she has grounds for killing Shepard if he's/she's a renegade. It would be cool to see a mission where you either recruit her or kill her depending on your alignment. I doubt Morinth will stick around if she's on the squad, since all she wants to do is

and kill.
Zaeed's gone since he was just a gun for hire. I imagine you'll hear about some of his adventures in ME3, though.
Legion is too important, even if he dies. The non-heretic Geth have at least had some contact with Shepard now. With how you handle Legion's loyalty mission, along with Tali's, it could shape out what kind of support Shepard is going to have in ME3, be it Quarian, Geth, or both.
I'd love to see Wrex back from ME1, but I doubt that's going to happen since he's got his hands full on Tuchanka.
I can see Liara also making a return as a squadmate to deal with the Shadow Broker. Plus, we've gotta have that romantic interest drama in ME3 to look forward to, which means that Ashley/Kaiden could be back, too.
I really hope we can assemble a sort of "dream team" in ME3. It wouldn't make sense to develop all of these characters and then just cast them aside for a brand new squad in ME3. Not saying that I don't want any new characters in the next game, but I want to feel rewarded for keeping my team alive.