Damn Small Linux, Puppy, Feather, Wolvix, Vector, STX, and Pocket Linux. Some of these can run entirely in memory and make applications running on old Pentiums fly.
Vector is very nice!
Slackware and Debian are not specifically designed for smaller or older machines. But, they allow lots of customization during installation and can fit minimal machines.
For laptops in particular []
Source: LinuxChick on []
Your host Walt gave up on gOS a couple of months ago, and has been running straight Ubuntu since.