iMode and cHTML
cHTML, or Compact HTML, is basically what WML should have been. Instead of completely new tags and new way of looking at things it's just a subset of HTML that makes sense for mobile devices. There are a few extensions to normal HTML but these aren't required and are very simple anyway (like using tel: in a link the same way you'd use mailto:).
Of course I don't really have any sites that would make sense ina mobile world...
Just search for imode chtml for loads of bits of info.