Comet technology

Server Push, long polling, Good descriptions here: http://code.google.com/p/google-web-toolkit-incubator/wiki/ServerPushFAQ
Maturity of Comet implementations: http://cometdaily.com/maturity.html
Best Comet/Streaming server: Caplin Liberator (http://www.caplin.com/caplin_liberator.php)