The first instinct may be to install Apache. However, nginx performs better on lower-end hardware. It should be noted that Apache can work just as well if the unnecessary plugins are removed and Apache is configured appropriately. For something that works fairly well out of the box, nginx is a great start.
# apt-get install nginx php5-fpm php5-mysql php-apc mysql-server
You will be prompted to set a password for MySQL; please make sure you remember it, as you will need it later.
# service nginx start