It appears Francois Bayrou, candidate from the centrist UDF (Union for French Democracy) Party, is making a bit of a run in the polls. Figures from yesterday put him at some 19%, which is well withing striking distance of the Socialist candidate Segolene Royale (25%) and Nicolas Sarkozy (29%), from the rightist UMP (Union for the Presidential Majority).
In an election system where only the two leading candidates advance from the first to the second (and final) round, Bayrou still falls short. There are a few wild cards in play which may skew the numbers -- most prominently Jean Marie Le Pen, the extreme right candidate. Voters typically have a tough time admitting to pollsters that they are about to vote for an immigrant-hating, Euro-phobic, ultra conservative whack job like Le Pen, but about 12% of them actually do in any given election (2002's election would be the exception to the rule, where Le Pen miraculously received 18,5% of the vote and snuck into the second round ahead of Lionel Jospin, the Socialist). While Le Pen may only poll at ~10%, these numbers are usually a bit lower.
The second (and related) issue, is the "heart vs. head" argument. With the two-round election, voters typically feel freer to vote their true feelings ("heart") in the first round (which leads to such a wide dispersal), but with only two candidates in the second, the masses are then shoe-horned into the more "logical" choice. Bayrou, as the centrist, probably doesn't stir the emotions enough to get voters enough to be the "heart" choice and get into the second round on that ticket.
But, hold the show for a minute -- there's a third consideration which may serve Bayrou well: With Sego embracing Mitterand's tactic in the 80s of running "hard left" during the first round -- to shore up the party base and avoid a Jospin-esque disaster from '02, and Sarko trying to pluck a few of Le Pen's supporters, there might just be a chance. If enough "center-center left" and "center-center right" voters decide that Sego and Sarko are pandering to their bases too much, there might be enough space in the political center for Bayrou to garner enough support to slip through. He has mentioned favoring a Socialist Prime Minister (whom he appoints), which helps his cause to steal from Sego...
It will be close, but, using Le Pen's '02 example, anything is possible.