I found a great overview of various GUI toolkits for Ruby but it's a bit 
old (2002 I think):

http://www.perfectxml.com/syngress/ruby/Page1.asp

Have any of you tried more than one GUI toolkit with Ruby?  If so, which 
do you prefer?

Also, are there GUI design tools or Ruby code generators for these 
toolkits that are "ahead of the pack" at the moment?

Looking forward to getting your opinions and preferences.

Thanks.