I am looking for a device that would allow me to remotely hard reboot my computer. The device could use either wired or wireless Internet connection. I just need to be able to remotely ask it to hard reboot the computer (e.g., physically pressing the power button).
The specific model's going to dependent on the style of plug you have locally. Depending on your specific needs, there's two options.
I've not used either of these personally (but I've been looking at them) but if you wanted a prebuilt minimal fuss wireless setup, belkin's WeMo has decent/mixed reviews. Their website is terrible but you're looking for something like this for your local voltage.
A lower cost option would be a rf controlled plug - this would be something similar to what I'd look for but once again, your exact options would depend on your local voltages and plugs. Quite a few folks have modded these for rpi control by rewiring the remote.