Try the games in
http://www.spin.de/
Also with Java 1.5 or newer (it works with 1.4.2!) you can try this:
http://www.radiogong.de/fileadmin/chat/
You can open private dialogs, but you are unable to close em. Very stupid bug...
There is already a open plugin based on the OpenJDK. It's called IcedTea. Look at http://iced-tea.org/wiki/Main_Page for information. Im using it on Gentoo x86_64 and it's worked very well so far, without any proprietary software needed.
@Kano: Are you reffering to IcedTea or one of the older free Java-replacements? Afaik IcedTea should be fully compatible. Maybe you'd tell us what sites you've got problems with?
Try the games in
http://www.spin.de/
Also with Java 1.5 or newer (it works with 1.4.2!) you can try this:
http://www.radiogong.de/fileadmin/chat/
You can open private dialogs, but you are unable to close em. Very stupid bug...
@Zhick
both works with 1.4.2, the spin chat games work with 1.5 and 1.6 too. Btw. the radio gong chat works with win, so it is a Linux only problem...