This article at salon.com is by Paul Maslin, pollster for Howard Dean and for Bill Richardson. It provides a sobering look at the 17 states he sees as even possibly in play this cycle:
Critics scoff and call it an antiquated and unfair system (it is). Many Democrats -- notably, this year, Obama backers -- would like their party to stop thinking in terms of three yards and a cloud of purple-state dust and instead embrace the beauty of a 50-state strategy. Somehow, they say, 2008 can and must be different.
OK, I'm listening. Different how? In that the Democrats win?
Certain cold realities haven't changed. A candidate must still reach 270 electoral votes to gain the White House. Unless there is a popular-vote landslide in November, the presidential election is still best seen as a collection of 50 statewide contests. Should this fall's election be as close as the last two in 2000 and 2004, no more than one-third of those 50 states will be in serious contention. In fact, only about half of that number will ultimately decide the outcome, since the vast majority of the other "close" states actually lean pretty strongly to one side or the other and are unlikely to shift their preference. Once again we're all going to be spending a lot of the next six months, at least psychically, in the Rust Belt.
http://www.salon.com/opinion/feature/2008/05/16/270/