Bruce Eckel has an in-depth article on the language/platform of choice for RIAs (rich internet applications). Although Java (with applets) was arguably the first-mover in this space, it lost out because of a bunch of issues (difficult to install, parts not well thought out, etc) which he has dissected. He contrasts this with JavaScript and AJAX which is clearly the winner right now.
However, he goes on to say that AJAX is essentially a hack that has reached its limits and is unlikely to go much further. It will run out of steam and the technology likely to take over is Flash (with Flex as the tool for creating rich Flash apps).
Very interesting reading even if you don’t agree with him.