There is a new and interesting remote administration application I'm trying called Web Console. It's sort of a blend of SSH and a file manager embedded in a Web browser. With SSH, VNC, FreeNX, and such you have to install both server and client components. With Web Console all you need is any modern graphical Web browser on the client side. I suppose it could work with text browsers that support AJAX, though I haven't tried any yet.

Setting it up on your servers, or whatever machines you want to administer remotely, is easy or hard depending on how familiar you are with running an HTTP server. Web Console is a Perl script, so it runs on any operating system that supports Perl and an HTTP server. Security is a bit tricky because, like any CGI script, it runs under your HTTP user. This can be a problem because Web Console lets you run pretty much any command you want, and that is not something you want your HTTP user to do. Apache users can get around with this suexec, which has its own perils if you're not careful.

You can encrypt your Web Console sessions with SSL, which I think should be the default behavior. I wouldn't use it beyond the LAN, but for inside the LAN it's fast and useful.
http://www.web-console.org/about/