The most dynamic and easily updateable websites are all driven by a database. This enables maximum flexibility and lowest possible maintenance because it completely separates content from presentation.

MySQL

A widely used free database is MySQL. It is both efficient and powerful, and has many fans all over the world. Most common scripting languages can be used with it, but the combination PHP/MySQL is most popular. Because of this, PHP/MySQL-hosting is most common on Linux servers, and since Linux, MySQL and PHP are both free and very efficient(less strain on the server), PHP/MySQL hosting is cheap.there are plenty of MySQL-driven PHP scripts available for free on the internet, like discussion forums, directory scripts and shopping carts.

PHP/MySQL-hosting is most common on Linux servers, and since Linux, MySQL and PHP are both free and very efficient(less strain on the server), PHP/MySQL hosting is cheap.

PostgreSQL

MySql's little brother in the open source world in terms of popularity, but very comparable(if not better) in performance.

PostgreSql hosting is also most common on Linux/Unix servers, since the Windows version is "on the way". Can easily be used with programming languages such as Python, PHP and Java. Does not add any significant costs to your web hosting account, but availability as a bit limited.

MS SQL

Microsoft has its own version of SQL, called MS SQL. Like MySQL it is a powerful database solution, but only available on Windows servers. Widely used for commercial applications, but Windows/MS SQL hosting is more expensive than Linux/MySql hosting, and there are fewer online resources for MS SQL.

Microsoft Access

One more database from Microsoft, which is available in many cheap Windows hosting packages. It is said not to be as efficient and scalable as SQL databases, but price is its strength if you need Windows hosting.