SliTaz Linux
This is an interesting, full-featured, lightweight Linux distro that was "built from scratch" by a team in Switzerland (and available in several languages). It has an attractive, polished GUI and good hardware support. Their website contains a large amount of excellent documentation, too.
SliTaz can be customized with additional packages from its large repository (more than 2000 packages). You can also choose from a few customized installs (or roll your own) scaled up or down to fit the limitations of your hardware, including one that I've run in a laptop with 48 MB of RAM and a 1.3 GB hard drive.
Even on old, slow, limited hardware it runs fairly fast without requiring a lot of configuration or customizations -- and it looks good (the 'spider' logo notwithstanding).
