Linux is available in several formats, called distributions. Each distribution has its own set of features and functionality that makes it unique -- some distributions are available for download at no charge, others are provided on CD or DVD and have a (usually) nominal charge associated with them. Below you will find links to web sites not only applications, tools, and utilities, but providing support, reviews, and other useful information.

Linux.org
Sourceforge.net
Linuxappfinder
Bellevuelinux.org
Bima.astro.umd.edu
Products.enterpriseitplanet
Icewalkers