Various services are web-apps. So running apache is a no-brainer. Also this server is where I have my different private projects and the test-bed for this homepage. Which implies that I have both python and php5 enabled in the server.
I am also using mysql for the database, maybe I will check postgresql sometime in the future.
Another service I run on the web-server is my version control system (provided with subversion). I have different repositories for my private data, my programming projects and my web-projects.