Here's my list and rankings in order from most likely to least likely
1. Ed Harris (nominated: Apollo 13, Truman Show, Pollock, Hours) He does so many character parts and still is prolific and is gaining a great reputation in Hollywood after having directed more of his own stuff. He still hasn't won and he's historically been able to score noms for very small and minor stuff. He also chooses roles wisely.
2. Ben Kingsley (nominated Gandhi, Bugsy, Sexy Beast, House of Sand and Fog) He's too brilliant, too prolific, and is getting too many juicy parts not to have something happen soon. He doesn't overdo it but he's had a leading rule in at least one film a year.
3. Geoffrey Rush (Shine, Shakespeare in Love, Quills, King's Speech)-There's a big danger of him being overshadowed by other Brits like Collin Firth, Clive Owen, Jude Law or whoever the next big one is but I think he's fairly hot again after being in the King's Speech so in the next year or two he might get #5 (and I say that with no clue what he's doing next)
4. Daniel Day-Lewis (My Left Foot, In the Name of the Father, Gangs of New York, There Will be Blood)-He's clearly capable of brilliance that makes everyone's jaw drop. The argument against is he's so sporadic and he can turn in a brilliant performance and just have it be in a highly competitive year or whatever. He's not making as many proverbial plate appearances
5. Jon Voight (Midnight Cowboy, Coming Home, Runaway Train, Ali)-He is a little bit over the hill, but I'd say he's one of the 2 or 3 most capable actors over the last decade for someone of his age range. He's in a lot of films and while a lot of them are Blockbusters (i.e. Transformers, National Treasure) I don't see him selling out to the levels of Robert De Niro (unless you consider his comedic acting a virtue). Also, unlike De Niro or Pacino, he doesn't have to fight a former image of himself and run into the wrap that he's doing a caricature of his former self. As a character actor, he gets better as he's less tethered than those two, and on top of that he acts pretty regularly and even in mediocre movies (Enemy of the State, Transformers) he steals scenes.
6. Anthony Hopkins (Silence of the Lambs, Remains of the Day, Nixon, Amistad)-I see it as unlikely. Even though he's been prolific and chooses varied roles, he hasn't got any buzz for anything he's done since nomination 4. I suppose it's not his fault that Bobby, Hearts in Atlantis, Proof, or All the King's Men didn't pan out well.
7. Robin Williams-I think he's already done dark performances and comic performances and inspirationally uplifting performances and there's not a whole lot he can do. There's not the same novelty to Robin Williams bringing out his (still incredible by any standard) rapid-fire multiple-voice comic persona that got him his first nod for Good Morning Vietnam.
8. Warren Beatty (Bonnie and Clyde, Heaven can Wait, Reds, Bugsy)-Already had his Oscar and lifetime achievement award and as Bullworth showed, he's more likely to get it in the directing or writing category these days.
Of the Actresses:
1. Julianne Moore (Boogie Nights, End of the Affair, Hours, Far From Heaven)-Way overdue for a nom on top of being overdue for an Oscar. Great actress who is regularly doing quality work and usually one of the 3 or 4 people anyone producing a film with potential Oscar buzz will go to first.
2. Helen Mirren (Madness of King George, Gosford Park, The Queen, The Last Station)-She's highly popular and is still getting prime roles and she's not as old as people think she is (she's just 66). Her being positioned up this high on my list, however, signifies my lack of confidence for anyone on this list other than Moore.
3. Annette Bening (Bugsy, American Beauty, Being Julia, The Kids Are All Right)-She's still due for an Oscar but I don't they'll nominate her unless there's a good chance she'll win. I also don't think it's likely that her next project will get her a nomination. It might might be a couple years before she's on the radar again.
4. Frances McDormand (Mississippi Burning, Fargo, Almost Famous, North Country)-She's still doing really good work and working with lots of inventive directors. She's older but hasn't been held back in any way by aging as some actresses are (i.e. Michelle Pfieffer, Meg Ryan).
5. Emma Thompson (Howard's End, Shadowlands, Remains of the Day, Sense and Sensibility)-Thompson was much bigger in the 90's than she is now but she still does quality level work, although it is now in films that are less visible (see "Brideshead Revisited). If the Academy is all of a sudden willing to go back to women like Redgrave and Close who haven't been considered for an Oscar in years, then there's no reason that if Thompson does something really impressive, it will go unnoticed
6. Holly Hunter (Broadcast News, Piano, The Firm, Thirteen)-She's been nominated far more recently than Thompson and is a favorite of the Coen brothers (who have lately been producing more Oscar nominees) but she works pretty infrequntly and is drawn to indepedent below-the-radar films. It was a wonder many people caught on to her fourth nomination in "Thirteen" at all.
7. Dianne Keaton (Marvin's Room, Annie Hall, Reds, Something's Gotta Give)-She already got her nod for showing that old people can be attractive, sexy, and appealling in movies. She can't play that card again.