Dotdeb is a repository containing packages to turn your Debian boxes into powerful, stable and up-to-date LAMP servers :

Nginx,
PHP5.5, 5.4 and 5.3,
useful PHP extensions : APC, imagick, Pinba, xcache, Xdebug, XHprof…
MySQL 5.5 and 5.6
Percona toolkit,
Redis,
Zabbix,
Passenger…
Dotdeb supports :

Debian 6.0 “Squeeze“

# main repository
deb http://packages.dotdeb.org squeeze all

# PHP 5.4
deb http://packages.dotdeb.org squeeze-php54 all

wget http://www.dotdeb.org/dotdeb.gpg
apt-key add dotdeb.gpg

apt-get remove --purge php*

apt-get install -t squeeze-php54 php5 php5-mysql php5-imagick php5-json

/etc/init.d/apache2 restart