PC control of ardunio via serial... best way?

I'm a halloween prop builder, and came across the Ardunio Mega last year, and about squealed with excitement. The halloween display I made last year that was controlled by this little godsend was amazing.

I'm making a new display this year, and was hoping to have one prop be a little more interactive. Last year, everything was pre-programmed, and ran on routines actived by motion sensor, or me pressing a button on a small control box. I'd like one prop this year to be a little more controlled if I want to take control of it. Specifically, making it talk. I want to use it as a soundboard.

Now, I already have the sound down. Bought this little beauty last year to control my zombie sound effects:

I control it via serial connection from the ardunio. Tell it which MP3 file to play from the on-board SD card. It's awesome.

However, I'd like to control the arduno from... something. A PC, my ipad, something. Instead of building a contol box and using up 30+ pins and having 30+ wires running to digital inputs, I thought I'd run a serial connection to the ardunio.

Question is - whats the best way to do that? I was thinking of maybe making a webpage that, via using PHP, sent serial commands to the ardunio. That was a thought. I also know there are bluetooth and wifi adapters for the ardunio but I've never even glanced at them, so I'm unsure what I can do with those... can I get a wifi or ethernet for the ardunio and send it control commands that way?

If you were building something that needed external control, whats the best way to do that? Is there some ipad app I can customize to send commands to an ardunio? By what method?

Thanks!

I just searched for arduino on my ipad and found Ardumote - totally custom remote control software using UDP. I may look into that option instead of serial. Will cost more as I'll need an ethernet or wifi shield, but, MUCH more versatile.

Maybe Im missing something- is there an issue to just controlling it over serial from the computer? If you dont like using a serial terminal program, you can even write a custom program in any language of your choosing to communicate over serial. If you buy an ethernet or wifi shield you should set them up as a web server, so you have complete control from the interface, and then it can be accessed from any web-connected device in your network.

You can put the apache web server on your pc and use it to make the serial/web connection to your prop.