For ultimate flexibility you can always try Berlitz in Lausanne. I've been taking private lessons there for a month now and I can book when I like, and cancel with a days notice. Teachers are great (you can insist on the same one if you find one you particularly like) and with 1-2-1 teaching I feel that I've learned more in a month than in a year from books/cds.

Bit expensive though as you need to pay up front for 36 lessons..

Andrew.