Not sure if it's OK to talk about betting on here (disclaimer: I think it's fun but it is a mugs game and a certain percentage of people WILL get addicted to it) but last time I looked the dems were 2/9 to win the popular vote which seemed a good bet to me.
Winner is a coin toss IMO. Last time there was a nice arbitrage to be had on election night itself as the Republican states declare first (stop the count!). I think last time you could've got both candidates at 4/1 in the space of 24 hours.