Freecode.com (AKA Freshmeat) was the original software release tracker, and is still available as archive.

DistroWatch Does as it says and tracks new and upcoming BSD / Linux / GNU / Solaris distribution releases.

Free Software directory is the FSFs Wiki to summarize FLOSS packages and projects.

GitHub is a prettier frontend onto git source control. Less suited for end users, but still allows searching for software.

Launchpad is the development hub for Ubuntu and also lists a few things that haven't made it into the package managers yet.

Linux Games Captures progress and newly released gaming software for Linux.

Linux Alternatives Curates a list of Linux software alternatives for migrating newcomers.

Wikipedia: List of free and open source software packages summarizes a few common names.

Sourceforge.net Is the classic open source development service and still home to and primary hub for many projects.