If you want to run without X11, debian 'stable' is the best on a laptop. Well, even with X11 if you don't want to run snazy stuff (google earth etc). I ran Debian unstable for /years/ on a toshiba Portégé 3480 with a 600Mhz PIII, 192MB memory, 6GB disk. I did extensive c++ programming with it too, with X11 etc.
If you want to run it without X11, it's even better. That old portégé is now running debian stable, with the screen off and two Cardbus ethernet and acts as a router on my LAN... still has a lot to give, and with a bit of care at configuration you can have the disk 'sleeping' 99% of the time and it's virtualy silent.