The polling is (should be) done, and the vote takes place tonight at the Iowa caucuses.
Republicans: Donald Trump has led in all recent polls, averaging a four point margin over Ted Cruz in the last five polls. Rubio has been gaining some momentum in recent surveys, although the 'gold star' Iowa poll out over the weekend had him well back of Cruz and Trump. It wouldn't be terribly surprising if there was a very close 3-way battle tonight; perhaps with Trump, Cruz and Rubio finishing within 5% of each other.
Democrats: Polls have varied widely in this race, although many of the most recent ones have shown a slight lead for Hillary Clinton. It appears that turnout for the Sanders campaign will be crucial in determining whether the Vermont Senator can score an important early win. Either way, it is looking good for Sanders in next week's New Hampshire primary. A new poll out this AM has him up by 31 points over Clinton.