Argentina 3, Brazil 2.
1. Messi vs Robinho. They won't be playing against each other, but they are the players that the other defense has to figure out. At this moment, no team has done that yet. Great runs & great shots don't necessarily lead to goals, but they do scare the shit out of the defense. Look for the backline of both teams to be obsessing over these players. And if they don't, well then you get goals like this.
2. Defense and Goaltending. Brazil has yet to come up with a great stop this tournament. I don't think they'll get in the final. Argentina's defense is tougher, a bit rougher, and while it may give up a free kick (and possibly a goal in said free kick) it would not let someone wander in unmolested.
3. Central Midfield--Riquelme will be the difference in this game. Look for a perfectly weighted assist, or the pass before the assist, or the goal itself. Riquelme will be the difference.