Once again, the PECL installer. In order to get the Mongo driver for PHP working, you need to install it manually.
mkdir mongo cd mongo wget https://github.com/mongodb/mongo-php-driver/zipball/master unzip master cd mongodb-mongo-php-driver-df8b217 phpize ./configure make install
Add the extension to your php.ini file.
extension=mongo.so
Restart Apache, and Mongo should appear inf your phpinfo() output.