I'm looking for a reliable, web-based IRC client that uses only port 80 on the client machine.

Ideally, all the hard work should be done on the web server with minimal scripting required on the browser (preferably in javascript using only what the common browser Document Object Model offers). I've seen one successful attempt at this (http://ezweb42.talkcity.com). However, it's really only a "proof of concept" (and it has problems when not running in Netscape). I'm looking for something that acts much more like a "real" IRC client.

You win no prizes for offering java solutions that connect directly from the client to the irc server on port 6667 (etc). You also fail to help by pointing to server- and/or channel-locked facilities (unless done so badly the lock-down can be circumvented :-).

Why? Port 80 is never going to be blocked by your ISP...