This Instructable is now depreciated.
Click here for the updated, much improved, version.
This will hopefully show you how to control electronics across the internet using your Raspberry Pi.
It's not the best way to do it, and soon I will update this with a way to use MySQL to do the same thing.
Here's a link to YouTube showing it in action: http://www.youtube.com/watch?v=OCZlfAFcm7Q
For this, please ensure that you have apache with php running on your Raspberry Pi, Instructions can be found here.
Also, it would be a good idea to read my previous instructable on general GPIO control, which can be found here.
Step 1: Overview + Warning
Until then, I'd recommend keeping this to your local network (not over the internet yet).
However, there shouldn't be any issues, it's just a warning. :D
This will (at the moment) allow you to control your GPIO pins via a web interface.
The program running on your Raspberry Pi checks to see if a file exists, if it does - it turns the output on, otherwise it turns it off. All the web interface does (at the moment) is to either create or delete this file.
Step 2: Web Page Code
As earlier, you will need Apache and PHP installed onto your Raspberry Pi (A guide can be found here).
The php code is attached to this step, and must be uploaded to the raspberry pi (/var/www/ directory).