How to read AC with Arduino?

Hi,

How can I read the AC with Arduino? I need only to check if some AC device on or off is...

There is no problem with DC, but AC?

I was pointed to a nifty style of optoisolator like this one that is designed for an AC input (with a resistor and a capacitor on the AC side). They're on the digikey order I've been working up (getting past that minimum order amount before I place an order).

-j