The latest Ifop poll (Le Monde article) seems to suggest Sarko would be the primary beneficiary if Le Pen isn't on the ballot:

Sarko: 28% (-1)
Bayrou: 23% (+4)
Royal: 23% (-2.5)
Le Pen: 13% (+1)
(Villiers: 1%)

Without Le Pen:
Sarko: 34.5%
Bayrou: 25%
Royal: 24%
(Villiers: 3.5%)

Doesn't take a denouncement by Le Pen into account of course. That's the first poll putting Bayrou at parity with Royal.

"The basis of optimism is sheer terror" - Oscar Wilde