When building a website with PHP, there are many frameworks you can choose from. However, they usually are very advanced with tons of features and sometimes a steep learning curve. If your needs are simple but you’d still like to build you site in a modular MVC-based fashion, PHP-MVC is a nice, light-weight alternative. You can learn more about it at https://github.com/panique/php-mvc.
Below is a screenshot showing you how simple the file structure is.
Update: another nice and simple PHP MVC framework is Simple MVC Framework.
which include some key plugins / extensions like PDO for safe, database-agnostic SQL and GUMP for form input validation.