Since today the plugin Creative Tag Cloud is available for free from the WordPress repository. It provides two tag clouds, one of them showing tags in a spiral and the other one in waves. You can insert them with shortcodes or widgets.
The code is based on the former plugin Chatty Mango Tag Cloud. I created it some time ago when I tested ways how to arrange tags in unusual ways. The main challenge has always been how to let the plugin automatically determine the best choice of parameters.
Eventually I decided to publish the Creative Tag Cloud plugin for free under the GNU Public Licence because it might just be right plugin for people who want to tinker with settings.
And this is the wave tag cloud for this web site:
[creative_wave_tag_cloud color=1 number=50 height=400 waves=4 opacity_decay=.8 line_height_factor=2.2]