Edit your source.list file with the following repositories :

deb http://download.tuxfamily.org/osrdebian/ unstable compiz-fusion-git

Add the corresponding key with :

$ wget http://download.tuxfamily.org/syzygy42/8434D43A.gpg -O- | sudo apt-key add -

Compiz Fusion is really great and – so far – stable enough !