start.me - A Modern-day bookmark manager. A place for your favorites. A news feed (RSS) reader. A browser startpage. A portal for your team.
Ruby Toolbox - Explore and compare open source Ruby libraries
Protopage - The best iGoogle alternative. Chris Pirillo calls Protopage "The best designed".
AlternativeTo - AlternativeTo lets you find apps and software for Windows, Mac, Linux, iPhone, iPad, Android, Android Tablets, Web Apps, Online, Windows Tablets and more by recommending alternatives to apps you already know.
Netvibes - First personalized dashboard publishing platform for the Web. Digital life managment, Widget distribution services and brand observation rooms.
LibHunt - LibHunt tracks mentions of software libraries on relevant social networks. Based on that data, you can find the most popular projects and their alternatives.