I've been thinking about the season finale a bit.
I think it's pretty obvious nikki will die, and the other will probably be either sylar or maya. If sylar dies, then maya will be the new villian. If maya dies, sylar will be the villian once again. The latter is probably more likely. But the previews could have indicated maya killing sylar with her abilities.
Nikki will die like people have said because she doesn't have anywhere to go really. Also, in the preview we see monica and micah hugging in fright and micah screams and tears as they see a house go up in flames, probably with nikki inside.
I think one of the cliffhangers of the season will be the heroes going public. Finally! That by itself to me would be a great cliffhanger. How will the world react?
I also think in the preview, when we see Peter telling Adam that they should go destroy the virus, Peter had had a talk with Hiro while time was stopped and Hiro explained everything to him. So now Peter will pretend to Adam like he doesn't know, and then will try to kill adam, but adam will throw the virus up in the air and Adam escapes while Peter stops the virus from hitting the ground and breaking so that it doesn't spread.
I'm still disappointed with this season though. The writing has been very iffy in most of the episodes, and there have been a lot of holes, such as some of the ones suzerain mentioned.

