Repology - Multiple package repositories analyzer
DistroWatch - 9 hours ago - It does include a proprietary software set optimized for business users, students, researchers and developers." A list of features and further details can be found in the company's release announcement.
Anitya - A software release monitoring project.
DistroHunt - Donation-based and video-focused directory of Linux distributions
The LiveCD List - This site was created to help sort through the many LiveCDs available.
whohas - whohas is a command line tool that allows querying several package lists at once