What distribution are you using btw? For a minimalist DE, I would go with either IceWM or Openbox. If you like win95 look, IceWM is your go to. If you like crazy customizability, then go with Openbox.
Ohhh I almost forgot about xfce. It is lightweight but still has the eye candy of more heavy DEs. Is also customizable, but not as much as Openbox.
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I'm actually a fan of old redhat or mandrake, but I think ubuntu is feature-full.
Now before any of you uber geeks jump down my throat for ubuntu, I'm one with old skool HP-UX and AIX, so step off, bitches.
Although, I didn't like how some of the basic system commands are hidden from default ubuntu (pick a distro, any distro), so this might not meet your "customizable" requirement.
Gnome or KDE?
I've been leaning towards XFCE, yeah. Openbox is just a window manager, not a desktop environment, so I can always use it with XFCE if I like.
<serious>
Now before any of you uber geeks jump down my throat for ubuntu, I'm one with old skool HP-UX and AIX, so step off, bitches.