SUSE - short for "System- und Software Elektronik"
Red Hat - named after the founders mark, a red fedora he came to work with.
Fedora - Spin off from Red Hat, kept the fedora-hat idea
Debian - AFAIK it is a mixture from the names Deborah and Ian
Yoper - Your OPERating system. No further explanation needed, I guess.
Mandrake - Named after the wizard Mandrake as it worked "magically", after the merging with Conectiva (Brazil) they became Mandriva.
Knoppix - Named after Klaus Knopper. Knopp + X = Knoppix.
Kanotix - Similar to Knoppix, named after Kano, the developer.
Linspire - originally named Lindows (guess why?

), had some legal problems with some well known company, then renamed to Linspire. Linux inspiration.