Election after election, the nominee has been the guy who was best-positioned to win at the beginning of the calendar year before the election. Before anyone declared their candidacy. Before all the sniping and scuffling between candidates began.
George W. Bush was widely seen as the front-runner (though I'm still not clear why) at the start of 1999. Bob Dole was the already the guy to beat at the beginning of 1995. It was generally assumed that Vice President Bush would be his party's nominee when 1987 began. Ronald Reagan was the front-runner for the 1980 nomination before 1979 even began. Elected or not, Gerald Ford was the incumbent and thus clearly the most likely pick for the 1976 nomination. Richard Nixon was seen as the likeliest 1968 nominee even in early 1967.
If there's an exception to this, it's John McCain in 2008, but I'm not sure he counts. From what I recall, at the start of 2007 McCain was widely expected to be the eventual nominee. Then, over the course of that year, his star faded as pundits decided he was running a lackluster campaign, and Romney and Giuliani and Fred Thompson rose in prominence. When the primary season actually started and McCain vanquished all his challengers within a month, it looked like he was coming from behind, but actually he was reclaiming his former spot.
If this pattern holds, the 2012 nominee will be the most boringly obvious of the current contenders. Half of the Republican Party is terrified of Palin. Huckabee is well-liked, but he's not taken seriously. Gingrich is taken seriously, but he's not well-liked. The other candidates will never be able to shake the perception that they're second-tier.
Obama vs. Mitt Romney in November 2012. It may be boring, but it's my prediction.