This radio is quite experimental and not hosted on LiveATC.net, but is a seriously nifty way to monitor HF. Unlike the other WebSDRs currently running, with several tens of kHz bandwidth, this one goes from DC to 19 MHz and receives really well. Sensitive, clean, and dead-on accurate. You can listen to one frequency and watch a whole aviation band at once - volmets, hfdl, voice, etc. http://websdr.ewi.utwente.nl:8903/
You may want to give this technology a try - it is quite cutting edge. PA3FWM hosts it at his home, with some limitations on bandwidth, so only a few users at a time can listen. Have fun!
(Listening to Gander / Shanwick on 8.891 MHz)