From what I have been reading, I reckon Brokeback Mountain is going to get a fair few, Heath Ledger is definitely in the running for a best actor oscar I think.
Not seen it myself yet to pass comment, but all the write ups I have read are very favourable
I hope Sin City gets recognised. It should do seeing as it was very original and was a critical and commercial success. However it will probably only get nominated for some bull$hit category like Best Sound Effects like these truly innovative films always do, (e.g. Fight Club).
I didn't think A History of Violence was particularly good personally. Sin City, Batman Begins and The Descent were probably the best films I watched last year. Saw II and War of the Worlds were ok too.