In the middle of my run-through of the individual states, I want to step back a bit, in an effort to see the forest, rather than the trees.
At this point, all indications point to a third consecutive presidential election that is decided by a small margin in the electoral college. For example, this New York Times projection currently puts 238 electoral votes in Obama's column, with 227 for McCain, and 73 labeled "toss-up".
The most interesting clump of toss-up or "leaning" states consists of Ohio, Michigan and Pennsylvania. There are other states that look uncertain, especially in the Upper Midwest and the West. But those three have 58 electoral votes between them, so it's more important to consider which way they're headed than to figure out Nevada or New Mexico.
One implication of their being Rust Belt states is that they don't have the population, and therefore the electoral votes, that they used to. Their current total of 58 electoral votes is meaningful, but in the 1950s they had 77.
But even with their reduced numbers, if either candidate can sweep those three, he would probably reach the magic number of 270 electoral votes.
Not that they'll necessarily all go the same way. In 2004, Bush carried Ohio by a small margin, which was the state that was considered to have put him over the top. Meanwhile, Kerry was winning Pennsylvania by an even-smaller margin. Kerry also won Michigan.