Abyss Web Server lets you run your own web server on your Mac. If you run a website, and also run your Mac 24/7, then you might be in for some savings. Abyss Web Server is a very advanced, stable and customizable web server that lets you turn your Mac into a web server. Installation is as easy as it could be. Simply running the .app file will install and launch the web server. Then all you have to do is go into the configuration console and point the app to where your website is on your hard drive and you are done. You access the console by typing in 127.0.0.1:9999 on your web browser address bar. Some of the settings include aliases, custom error pages, scripting, access control, IP address control, bandwidth limits and anti-leeching. There is also a very complete statistics system that you can access from the console.
This server can run PHP, Perl, Python, ASP, and ASP.NET web applications and it even supports databases. I have read countless reviews by other users who say it is very easy to configure PHP on this server.
By default, your website will run on port 8000, but you can change this from the settings.
There is a lot of help on the website that should let you solve any problems you have. And there are also good reads about how to customize the web server.