Why the disdain for redhat?
In addition to Ubuntu(mint is an offshoot of ubuntu IIRC) there’s also live cd offerings from suse.
Many smaller distros offer live cds as well, such as sabayon.(which is tailored towards gamers)
Good luck with your portable.
Everyone seems like Ubuntu/Kubuntu and a few others, so I hope to be to try one of those, or Fedora 12 of course, soon.