You can buy an ethernet shield of any kind, ENC28J60, wifi module etc etc, and NOT do the html on the chip, just set it up as a server (usually specific the the shield/module you use). 

Then you can actually create a local html file on your computer, or even use any webserver on your network or even online. As long as you send the commands to the local address of your arduino.

So if your Arduino ethernet module has the IP-address: 192.168.1.123 then the following form will send a command to the arduino that you can handle in the arduino code:

 <form action="http://192.168.1.123/acommand=1">
 <input type="submit" value="click to send command">
 </form>


So if you create a simple web form to send a command to the arduino you can put this page anywhere, as long as the action is pointing at your arduino IP-address. If you want to go into the whole jquery standard it might be a bit different, unsure how asyncronious submits are handled.

I want to point out that IF you put your simple html page online you dont need to and SHOULDNT open anything in your firewall or router. The code will work as long as the device you are accessing the page from is on the same network as your arduino.