MindTerm (which Xan suggested) rocks. (It's great!)
I've been using it for close to 8-10 years now. Mostly, I use it to access my box when I'm travelling and have only access to a web browser at an internet cafe or hotel.
vt100 emulation appears to be even more improved in version 3 -- I just tried the latest code. It also supports sftp, sshd-X11 forwarding, and a bunch of other neat stuff, too.
Version 3.1.2 is available for download now; more info on configurable options and its features:
http://www.appgate.com/products/80_Mind ... _MindTerm/
All you need is a single .jar file, a single HTML file, a web server, and a web browser. You can also run it as a Java application without a web browser, too, if you've got a local JRE. Handy for lugging around on a thumbdrive, perhaps? Avoids the need to install a ssh application on an untrusted PC.
The free MindTerm distributed is unsigned. That means you can't connect to a ssh server other than the web server that served it. This is good because it avoids abuse by others whom wanted to use my ssh server to hack other sites. Downside is that file transfers are also disabled (also due to the Java security model) if applet is unsigned.
You've got choices, though: you can always self-sign the applet. The developers even provide a link on how to accomplish this! Alternatively, starting with Java 1.6, you can also create a simple file on the local PC that gives it permission to do file operations to/from that web server without needing to sign the applet.
If you want to sign the applet, general instructions can be found here:
http://mindprod.com/jgloss/signedapplets.html