I guess the obvious one would be CSU-FPD, but I ask since long time rule can produce some strange dynamics.
In Sweden, in some local elections the Social democrats held majority for a long time and once they lost it they acted so pompously in the negotiations that the result has been everybody-but-the-soc.dem. coalitions. And that includes every party from the communists to the marketistas. A vote for PES is a vote for EPP! A vote for EPP is a vote for PES! Support the coalition, vote EPP-PES in 2009!
But, I don't really expect a permanent dent in CSU's fortunes... except if Huber carries his economic liberalism too far too fast. *Lunatic*, n. One whose delusions are out of fashion.