Pack200 and "deflate" are the only ones that are supported in java out-of-the-box. Though you can write a
that reads from other archive format such as BZip2 or 7z (LZMA), it requires to be present in a start-up stub applet, that contains the Classloader, downloads the archive containing main application, loads the classes from it and starts the app.
With Bzip2 or LZMA, you can get a better compression ratio than pack200, upto ~50%
It explains how to load from a jar, but same approach can be used to load from other types of archives too, take a look at Apache's Commons Compress, it has nice support for various archive types.