Last night my printer printed out a blank sheet of paper... which is normally fine... but it was not on! It's a wireless printer and is hooked up to my home's wireless network; but I'm not sure if a network glitch could cause this. There was no sort of power surge or anything. I would love to hear that there is some sort of technological explanation, otherwise I might need to head on over to the paranormal discussion board!

"hooked up to my home's wireless network"

I think this would be the most likely reason. The printer received a signal from some device and responded. Are you in an area where there lots of wireless devices (like an apartment/condo complex or something?). You might change the pass key or the channel if this persists.
Dwight

I live in a somewhat rural area and only have three close neighbors, none of whom even have internet access in their homes. The closest neighbor other than them is about a quarter of a mile down the road. Why would it receive a signal when it wasn't on though? Wouldn't it need to be on to respond?

If the printer was not on, it would not receive a command. Is it possible that it had a print command in the print queue that had not cleared before shutting down and then printed when it was turned back on? force clear print queue

Does this printer have a connection for updating itself via the Web? If so, the page may have printed as a result of a program update. (This assumes the printer was not actually off but rather in a energy savng mode).

You might try contacting the maker of the printer or look on their support page to see if they make any reference to background updates.

Do you have a 3rd party firewall installed? This is a firewall other than the built in windows firewall. If not, you might consider installing one to block any unauthorized access to your system. A free one is available for home use from ZoneLabs.
Free Firewall