Am staying at the Holiday Inn St.Germain des Pres. Really convenient location and close to the Metro. 190Eur a night, which is not too bad in Paris.
On a side note, I think that the reason that hotels are so booked is also due to the Formula 1 Grand Prix de France 2008 at Magny-Cour just outside Paris being run this weekend. It is big event. May go and watch the qualifying on Saturday! Looks like it is busy weekend in Paris.