Aptosid, formerly Sidux, is one of my favourite distributions. Like Ubuntu
is is based on Debian unstable, and like Ubuntu it is thoroughly tested. It
is faster than Ubuntu, but not quite as easy to configure. It has big
repositories because it is Debian, but not as big as Ubuntu's. It is the
distribution that I personally would use if I was not a Kubuntu user. I
don't recommend it often because most new users like something with more
support and the Debian community is shark infested waters. There are many
great people, but lots of people on a crusade, and it is hard to avoid them.

Debian itself will run on 128 MBs of RAM, but KDE is probably going to use
more than that. I think trying LXDE or Openbox on the Aptosid base would be
very good for low RAM.

I did not like the name change, but am getting used to it. Sidux worked for
me. I think it is a German based distro, so perhaps it works better in
German. I think they spell it all lowercase which makes starting a sentence
with it awkward